Light concentrator module

ABSTRACT

The invention provides a lighting device ( 1 ) comprising a luminescent element ( 5 ) comprising an elongated light transmissive body ( 100 ), the elongated light transmissive body ( 100 ) comprising a side face ( 140 ), wherein the elongated light transmissive body ( 100 ) comprises a luminescent material ( 120 ) configured to convert at least part of a light source light ( 11 ) selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body ( 100 ) into luminescent material radiation ( 8 ). The invention further provides such luminescent element per se.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2018/068060, filed on Jul.4, 2018, which claims the benefit of International Application No.PCT/CN2017/092253, filed on Jul. 7, 2017 and European Patent ApplicationNo. 17188736.7, filed on Aug. 31, 2017. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a lighting device, such as for use in aprojector or for use in stage lighting, comprising an elongated lighttransmissive body. The invention also relates to a lighting system suchas a projection system or luminaire.

BACKGROUND OF THE INVENTION

Luminescent rods are known in the art. WO2006/054203, for instance,describes a light emitting device comprising at least one LED whichemits light in the wavelength range of >220 nm to <550 nm and at leastone conversion structure placed towards the at least one LED withoutoptical contact, which converts at least partly the light from the atleast one LED to light in the wavelength range of >300 nm to ≤1000 nm,characterized in that the at least one conversion structure has arefractive index n of >1.5 and <3 and the ratio A:E is >2:1 and<50000:1, where A and E are defined as follows: the at least oneconversion structure comprises at least one entrance surface, wherelight emitted by the at least one LED can enter the conversion structureand at least one exit surface, where light can exit the at least oneconversion structure, each of the at least one entrance surfaces havingan entrance surface area, the entrance surface area(s) being numbered A₁. . . A_(n) and each of the at least one exit surface(s) having an exitsurface area, the exit surface area(s) being numbered E₁ . . . E_(n) andthe sum of each of the at least one entrance surface(s) area(s) A beingA=A₁+A₂ . . . +A_(n) and the sum of each of the at least one exitsurface(s) area(s) E being E=E₁+E₂ . . . +E_(n).

US2010/124243 A1 discloses a semiconductor light emitting apparatus thatincludes an elongated hollow wavelength conversion tube havingwavelength conversion material dispersed therein. A semiconductor lightemitting device is oriented to emit light inside the elongated hollowwavelength conversion tube to impinge upon the elongated wavelengthconversion tube wall.

US2014/185269 A1 discloses a photoluminescent wavelength conversioncomponent and a lamp that incorporates such a component. Thephotoluminescence wavelength conversion component comprises a hollowcylindrical tube having a given bore of diameter and an axial length.The relative dimensions and shape of the component can affect the radialemission pattern of the component and are configured to give a requiredemission pattern (typically omnidirectional). The photoluminescencematerial can be homogeneously distributed throughout the volume of thecomponent during manufacture of the component.

US2010/053970 A1 discloses a light-emitting device that includes a firstlaser light source, a first diffusion member provided along a light axisof a first light radiated form the first laser light source, and a firstwavelength converter provided along the first diffusion member. Thefirst diffusion member generates a second light from the first light.The second light outgoes in a direction different from the light axisdirection of the first light. A ratio of generating the second lightfrom the first light in a first part is higher than that in a secondpart, wherein an intensity of the first light in the first part is lowerthan that in a second part. The first wavelength converter absorbs thesecond light and emitting a third light having a different wavelengthfrom the second light.

US2007/280622 A1 discloses a light guide that includes a material thatis capable of emitting light of a second wavelength when illuminatedwith light of a first wavelength where the first wavelength is differentfrom the second wavelength. The light guide further includes an exitface that has a first portion that is reflective at the secondwavelength and a second portion that is transmissive at the secondwavelength. When the light guide is illuminated with light of the firstwavelength, the material converts at least a portion of the light of thefirst wavelength into light of the second wavelength. The majority ofthe light of the second wavelength that exits the second portion of theexit face is totally internally reflected by the light guide.

SUMMARY OF THE INVENTION

High brightness light sources are interesting for various applicationsincluding spots, stage-lighting, headlamps and digital light projection,etc. For this purpose, it is possible to make use of so-called lightconcentrators where shorter wavelength light is converted to longerwavelengths in a highly transparent luminescent material. A rod of sucha transparent luminescent material can be illuminated by LEDs and/orlaser diodes (LDs) to produce longer wavelengths within the rod.Converted light which will stay in the luminescent material, such as a(trivalent cerium) doped garnet, in the waveguide mode and can then beextracted from one of the (smaller) surfaces leading to an intensitygain.

In embodiments, the light concentrator may comprise a rectangular bar(rod) of a phosphor doped, high refractive index garnet, capable toconvert blue light into green light and to collect this green light in asmall étendue output beam. The rectangular bar may have six surfaces,four large surfaces over the length of the bar forming the four sidewalls, and two smaller surfaces at the end of the bar, with one of thesesmaller surfaces forming the “nose” where the desired light is extracted(e.g. with an optical element).

Under e.g. blue light radiation, the blue light excites the phosphor,after the phosphor start to emit green light in all directions, assumingsome cerium comprising garnet applications. Since the phosphor isembedded in—in general—a high refractive index bar, a main part of theconverted (green) light is trapped into the high refractive index barand wave guided to the nose of the bar where the (green) light may leavethe bar. The amount of (green) light generated is proportional to theamount of blue light pumped into the bar. The longer the bar, the moreblue LED's (light emitting diodes) and/or laser diodes can be applied topump phosphor material in the bar and the number of blue LED's and/orlaser diodes to increase the brightness of the (green) light leaving atthe nose of the bar can be used. The phosphor converted light, however,can be split into two parts.

A first part consists of first types of light rays that will hit theside walls of the bar under angles larger than the critical angle ofreflection. These first light rays are trapped in the high refractiveindex bar and will traverse to the nose of the bar where it may leave asdesired light of the system.

Hence, it is an aspect of the invention to provide an alternativelighting device comprising a luminescent concentrator, which preferablyfurther at least partly obviates one or more of above-describeddrawbacks and/or which may have a relatively higher efficiency. Thepresent invention may have as object to overcome or ameliorate at leastone of the disadvantages of the prior art, or to provide a usefulalternative.

Therefore, in an aspect the invention provides a lighting device havinga luminescent element comprising an elongated light transmissive body,the elongated light transmissive body comprising a side face, wherein:(i) the elongated light transmissive body comprises a luminescentmaterial configured to convert at least part of a light source lightselected from one or more of the UV, visible light, and IR received bythe elongated light transmissive body into luminescent materialradiation; (ii) the elongated light transmissive body has a length (L);and (iii) the elongated light transmissive body is hollow over at leastpart of the length (L) thereby defining a cavity.

It appears that hollow elongated bodies may have higher efficientoutcoupling than massive elongated bodies. Especially, this may applyfor elongated bodies have an essentially circular cross-section, thoughfor non-circular cross-sections this may also apply.

Hence, in embodiments the elongated light transmissive body has apolygonal cross-section, wherein the elongated light transmissive bodycomprises a cavity surrounded by the elongated light transmissive body.Or, in other words, the material of the elongated light transmissivebody is configured such that there is a cavity with the material of theelongated body at least partially surrounding the cavity.

In yet other embodiments, the elongated light transmissive body istubular shaped. Therefore, in embodiments the elongated lighttransmissive body has a tubular shape having a cavity surrounded by theelongated light transmissive body.

Especially, the cavity has a cross-section having the same symmetry asthe cross-section of the elongated light transmissive body. Hence, atubular shaped elongated body having a circular cross-section may alsohave a cavity having a circular cross-section. Likewise, an elongatedbody having a polygonal cross-section may have a cavity also having apolygonal cross-section. Note that it is not necessarily the case thatthe cavity has a cross-section having the same symmetry as thecross-section of the elongated light transmissive body. Further, theedge(s) of the cavity may be configured essentially parallel to theedge(s) of the elongated light transmissive body. However, when theelongated light transmissive body tapers, in embodiments the edges ofthe cavity and the elongated body may not be necessarily parallel (seebelow). Further, the cavity may have the same length as the elongatedbody or may have a shorter length. In general, at least at one end face(herein in embodiments also indicated as first face and second face) theelongated body may have an opening to the cavity (like a vase).

Further improvements of the outcoupling may be achieved when the cavitycomprises a light transmissive material. Therefore, in embodiments atleast part of the cavity, especially the entire cavity, comprises alight transmissive material, differing in composition from thecomposition of the material of the elongated light transmissive body. Inspecific embodiments, the light transmissive material in the cavity hasan index of refraction equal to or lower than the light transmissivematerial of the light transmissive body. An example of a suitablefilling may comprise one or more of MgF₂ or CaF₂, silicone, glass ortransparent ceramics like spinel, poly-crystalline alumina, sapphire,YAG, a material similar (e.g. when the light transmissive body comprisesa garnet, the filling may also comprise a garnet, but based one or moreother constituents), or identical (e.g. same garnet material) to thefirst body material, but especially without the phosphor. The materialsshould especially be transparent, but could be amorphous,poly-crystalline or single crystalline.

The drawback of current HLD is that one cannot make use of leakage ofblue to make white light. However with the present invention it ispossible by making for example yellow light (green+blue) with outer rodand with inner rod one could generate blue. Especially, with no ornearly optical contact of the rods, the efficiency may be higher.

Blue light can be either added by putting high power blue LED/Laser infront of light guide which is put in the yellow rod. Or one could use ablue HLD rod in the center with 405 nm pumping LED. At the end of therods, if needed, mixing of light can be done. For theatre and stagelighting an etendue of 16 mm² sr such as commonly required for beamersis not necessary. An etendue of 500 mm² sr may be sufficient; may beobtained with bodies with a relatively large cross-sectional area. Alarger etendue allows more (low-power) light sources to pump the body.Further, it appears that cylindrical rods can be produced easier andthus also more reliable.

By putting various diameter cylindrical rods in each other one cangenerate white light without the use of expensive dichroic mirrors. Eventuning of the spectrum is possible. Also it can be done in an efficientand cost effective way because the making of round rods is in principlecheaper to make. Outside can be easily polished but inside it may bemore difficult for small and long rods. Still it seems that scatteringof inside rod has less negative effect as scattering at outside rod.

For facilitating incoupling of light, the tube diameter can be made abit larger and afterwards taper a bit towards the nose. Firstsimulations show that tapering from a relative diameter 1.00 to towardsa relative diameter of 0.60 is possible without essentially losing light(i.e. the diameter reduces towards the nose with 40%). Even, it may bebeneficial extracting a bit more light towards the desired direction.

Use of round shapes may imply an essentially round light distributionwhich is advantage for lighting applications. Rectangular hollow tubescan also be put together. To mix the colored light from the differentround tubes one could use an integrator element, such as especially anintegrator rod. For example, one may use FlyEye optics. Optionally, theintegrator element is comprised by (i.e. especially integrated in) theelongated light transmissive body. One could also attach this roundcombination first to a small piece of transparent (rectangular ordifferently shaped polygonal) tube in order to mix the light properlyand then attach the collimator, such as a CPC, or other optical element,such as a dome shaped optical element.

Hence, the luminescent element may further comprise an optical elementoptically coupled to the elongated light transmissive body such as aCPC. However, in yet other embodiments the optical element comprises aplurality (i.e. 2 or more) of optical fibers, optically coupled to theelongated light transmissive body. In yet further embodiments, theoutput side of the optical fibers may be coupled to yet another opticalelement, such as a collimator, such as a CPC, or other optical element,such as a dome shaped optical element.

Hence, the luminescent element may comprise a plurality of elongatedlight transmissive bodies. In embodiments, a single light transmissivebody together with the light source may provide white light. However, asindicated above, in general a single light transmissive body and one ormore (radiationally coupled) light sources may especially be configuredto provide colored light. Hence, when a plurality of elongated lighttransmissive bodies is applied, this may e.g. be used for providingwhite light (in a first mode of the lighting device; see further below).Therefore, also single-color systems, multi-color systems, off-BBL ornon-white color point, emitting luminescent elements may be provided.

Especially, as indicated above, when hollow elongated light transmissivebodies are applied, a smaller body may be configured in a cavity of alarger body. Therefore, in specific embodiments, the invention alsoprovides a luminescent element according to any one of the precedingclaims, comprising a plurality of elongated light transmissive bodies,each elongated light transmissive body comprising a luminescent materialconfigured to convert at least part of a light source light selectedfrom one or more of the UV, visible light, and IR received by theelongated light transmissive body into luminescent material radiation,wherein: (i) the elongated light transmissive bodies may differ in e.g.one or more of (a) length (L) of the elongated light transmissivebodies, (b) type of luminescent material, (c) concentration ofluminescent material, (d) concentration distribution over the elongatedlight transmissive body, and (e) host matrix for the luminescentmaterial; (ii) each elongated light transmissive body has an axis ofelongation (BA); (iii) one or more of the elongated light transmissivebodies comprise cavities; and wherein the elongated light transmissivebodies are configured in a core-shell configuration wherein a smallerelongated light transmissive body is at least partly configured in thecavity of a larger elongated light transmissive body and wherein theaxes of elongations (BA) are configured parallel. Alternatively oradditionally, the elongated light transmissive bodies may in embodimentsalso differ in one or more diameter and wall thickness.

The lengths of the elongated light transmissive bodies may essentiallybe the same, or may differ.

In specific embodiments, the elongated light transmissive bodies haveside faces, and wherein side faces of adjacent elongated lighttransmissive bodies have no physical contact or only over at maximum 10%of their respective surface areas.

In specific embodiments, the elongated light transmissive body has afirst face and a second face defining a length (L) of the elongatedlight transmissive body; wherein the side face comprises the radiationinput face, wherein the second face comprises the radiation exit window.

As indicated herein, the luminescent element may comprise a plurality oflight transmissive bodies. Therefore, in yet a further embodiment theinvention provides a lighting device as defined herein, comprising theluminescent element with a plurality of elongated light transmissiveelements, which are especially configured in a core-shell configuration,wherein the lighting device further comprising a plurality of lightsources, wherein one or more light sources are configured to providelight source light to the side face of an outer elongated lighttransmissive body and/or wherein one or more light sources areconfigured to provide light source light to one or more first faces,wherein the one or more first faces are end faces, and/or wherein one ormore light sources are configured in a cavity of an inner elongatedlight transmissive body and configured to provide light source light tothe side face of the inner elongated light transmissive body. Hence, inembodiments one or more light source may be configured to provide lightto an outer side face of an outer (shell) elongated light transmissivebody. Alternatively or additionally, in embodiments one or more lightsource may be configured to provide light to an inner side face of aninner (shell) elongated light transmissive body.

In embodiments, the multiple elongated bodies may be comprised by amonolithic body where the elongated bodies may not be physicallyseparate, but e.g. only have a different host matrix realized by e.g.2-component extrusion or 2-component injection molding; see alsoelsewhere.

Especially, in a first mode of operation the lighting device isconfigured to provide white light. However, the lighting device may alsobe configured to provide (in embodiments another mode of operation) toprovide colored light or infrared light. Especially when two or moreelongated bodies are applied, in embodiments the spectral distributionof the lighting device light (i.e. the light emanating from the lightingdevice) may be controllable.

Hence, in embodiments at least two elongated light transmissive bodiesprovide luminescent material light with different spectraldistributions. This may be used to provide e.g. colored light with e.g.a broad spectral distribution. Especially, the lighting device mayfurther comprise a control system, configured to control the spectraldistribution of the lighting device light. The phrase “with differentspectral distributions” may in embodiments refer to spectraldistributions having intensity averaged emission maxima at wavelengthsthat are position at least 10 nm, such as at least 20 nm from eachother.

A luminescent element with a plurality of elongated light transmissivebodies may comprise a plurality of optical elements. These may beconfigured downstream of the radiation exit faces. However, also anintegrated optical element may be used, that is configured downstream ofmore than one of the light transmissive bodies. This may be useful for acore-shell configuration, but also for a configuration wherein aplurality of elongated light transmissive bodies are configured in abundle kind of configuration.

Therefore, in embodiments the lighting device may further comprise anoptical element, wherein the optical element comprises a first wall anda second wall surrounding the first wall thereby defining an opticalelement having a ring-like cross-section, wherein the optical elementcomprises a radiation entrance window and a radiation exit window,wherein the radiation entrance window is optically coupled with theplurality of elongated light transmissive bodies. Such optical elementmay have a shape like a fluted tube or Bundt pan. However, other optionsmay also be possible (see below), wherein e.g. a tapering in a directionaway of the light transmissive body may be possible.

Light concentrators (herein also indicated as “elongated lighttransmissive body”, “transmissive body”, “luminescent concentrator”,“luminescent body”, or as “rod”) that may be used in e.g. HLD (highlumen density) light sources may have a rectangular cross section, and(blue LED and/or laser diodes) light from external can coupled-in in therod and converted by a phosphor to light of longer wavelength. Theemission of light by the phosphor is omnidirectional in a random way.That means that a part of the light leaves the rod immediately, bytransmission through one of the four long sides of the rod. This light,as a fraction of the total emitted light, is given by the solid angle ofthe four light cones in which the light has an angle with the rodsurface smaller than the critical TIR angle, as compared to the totalsolid angle of 4π.

For light concentrators based on YAG or analogous garnet material (seebelow) the refractive index is close to 1.84, and the solid angle of the4 cones together occupies 32% (disregarding reabsorption) of the wholespace. Assuming no reabsorption, this light can (to a large part) beconsidered as lost light, as even reflectors around the rod cannot helpto get light into total internal reflection (TIR) in the rod. It isimportant to note that the position of the light generation in the rodhas no implication for the relative light fractions.

Light concentrators can especially be used in combination with opticalelement for improving outcoupling of the light from the concentratorand/or for beam shaping. A choice for such optical element is an opticalconcentrator element, such as a compound parabolic concentrator (CPC)(see also below).

When using a high-index CPCs (n_CPC>1.55 in case of n_rod=1.84), some ofthe light that is generated very close to the CPC could either benon-TIR or could be coupled out via the CPC, dependent on the exactposition.

Hence, for a light concentrator with a n=1.52 CPC, three light fractionscan be discerned, namely Non-TIR light in the cones that are directlytransmitted through one of the four long sides.

Light in the cones that are aligned with the long axis (z-axis) of therod, this light sometimes is called TIR-to-Nose light, as this light isin TIR in the rod until it hits the CPC, and is transmitted through theCPC. The rays that go into the CPC have an angle with the z-axis that issmaller than the critical TIR angle that holds for the n_rod-n_CPCcombination. The light in the cone that is directed towards the tail mayat least partly reflect at the tail via TIR or via Fresnel, or via anexternal mirror (see also below), and also leaves the rod at the CPC.

The remaining light fraction is in TIR and—in theory, in a perfectrod—these rays cannot escape from the rod. This fraction is sometimescalled locked-in TIR light (after the Locked-in syndrome).

In case n_CPC=n_rod, this locked-in light fraction III does not exist,all the light that is in TIR is leaving the rod via the CPC.

In case n_CPC<n_rod, there is locked-in light, but in practice the lightis not contained in the rod forever, but is scattered after some length,or re-absorbed and re-emitted again, and if this happens in a randomway, eventually the light is redistributed over the fractions I and II.Under full randomization of the light by scattering, the fractions I andII are also the weighing factors for the redistribution of the locked-inlight. This is below also indicated in a table.

n_rod = 1.84, n_CPC = 1.52 Light fractions n_rod = 1.84, n_rod = 1.84,redistributed in rectangular rod n_CPC = 1.84 n_CPC = 1.52 Locked-In Inon-TIR 32% 32% 32% + 11% = 43% II TIR-to-Nose 68% 43% 43% + 14% = 57%III Locked-in TIR — 25% redistributed

Rods (up to now with rectangular cross section) are expected to have amaximum optical efficiency depending on the refractive index of the rod.If the optical efficiency is defined as the ratio of luminescentmaterial light that goes into the CPC over the total luminescentmaterial light generated in the elongated light transmissive body, thebelieved maximum is 68% in case of n_rod=n_CPC=1.84, and is lower, about57%, in case of a rod with n_rod=1.84 and n_CPC=1.52 (glass). In thelatter case, part of the locked-in fraction (III) is converted into theTIR-to-Nose fraction (II) via scattering or via re-absorption andre-emission.

Hence, it is an aspect of the invention to provide an alternativelighting device comprising a luminescent concentrator, which preferablyfurther at least partly obviates one or more of above-describeddrawbacks and/or which may have a relatively higher efficiency. Thepresent invention may have as object to overcome or ameliorate at leastone of the disadvantages of the prior art, or to provide a usefulalternative.

It appears that in a round rod the three light fractions have differentvalues. If the light is generated somewhere in the heart of the rod, thelight fraction I (non-TIR) is high. The light fraction II is still thesame as for a rectangular rod, and Locked-in Light is virtually notpresent. Further, it surprisingly appears that with n_rod=1.84, thelight fraction that is escaping from the rod directly (non-TIR) is only16% if it is generated in the skin of the rod (skin thickness=0). Iflight is generated on the skin, the non-TIR cone angles to both sidesperpendicular to the skin are identical for the round rod andrectangular rods, which can be proven by simple goniometry. For thatreason, the non-TIR fraction for skin generated light is exactly half ofthe non-TIR fraction in a rectangular rod. The non-TIR loss has beenmodelled analytically for round and rectangular rods. Assuming the lightto be generated at a distance x from the wall, the non-TIR fractionincreases with the relative distance to the wall, as expressed in theratio x/r, which is the case for round rods only. Further, itsurprisingly appears that up to about x/r=0.4 there is lower non-TIRlosses for round rounds as compared to rectangular rods. For a round rodof 2 mm diameter this is up to a depth of 0.4 mm.

The afore-mentioned consideration may not only apply to essentiallymassive CPCs as optical element downstream of the luminescentconcentrator, but may also apply for other optical elements, such as adome, a wedge-shaped structure, a hollow CPC, et cetera.

Hence, the invention provides in an aspect a luminescent elementcomprising an elongated light transmissive body, the elongated lighttransmissive body comprising a side face, wherein (i) the elongatedlight transmissive body comprises a luminescent material configured toconvert at least part of a light source light selected from one or moreof the UV, visible light, and IR received by the elongated lighttransmissive body into luminescent material radiation; (ii) the sideface comprises a curvature with a radius (r); and (iii) theconcentration of the luminescent material is chosen such that at least50%, such as at least 60%, like at least 70% of the light, especially atleast 80% of light, at one or more radiation wavelengths is absorbedwithin a first length (x) from the side face, wherein in specificembodiments especially x/r≤0.4 applies.

In the case of hollow light transmissive bodies or in the case of lighttransmissive bodies with a high luminescent material concentration in anouter region of the body and a lower concentration (including zero) at amore inner part of the body, such as a core, the concentration of theluminescent material may be lower, as radiation that is not absorbed mayescape from the body but be absorbed again. Hence, assumingperpendicular irradiation of the side face from external of the lighttransmissive body, thus not from inside in the cavity, the concentrationof the luminescent material may also be chosen such that at least 50% ofthe radiation, such as at least 60% of the radiation of the lightsource, like at least 70%, especially at least 80%, is absorbed. Here,the perpendicular radiation may thus especially include propagatingthrough a first region with relatively high concentration and beforeemanating from another part of the body also propagation through asecond region with relatively high concentration. Hence, in specificembodiments also for this configuration the concentration of luminescentmaterial may be chosen such that in total at least 50%, such as at least60%, like at least 70%, such as especially at least 80%, is absorbedwithin a first length (x) from the (outer) side face, wherein inspecific embodiments especially x/r≤0.4 applies, where r refers to theradius of the outer surface of the hollow light transmissive body.

With such element it may be possible to provide in a more efficient waylight, escaping from the transmissive body, when the transmissive bodyis illumination with light source light that is at least partiallyconverted by the luminescent material comprised by the transmissivebody. The outcoupling may be higher than in luminescent bodies having arectangular cross-section.

Especially, the concentration of the luminescent material is chosen suchthat at least 50%, such as at least 60%, like at least 70% of the light,especially at least 80% of light, at one or more radiation wavelengthsis absorbed within a first length (x) from the side face, whereinespecially x/r≤0.4 applies.

In embodiments, the radius (r) is selected from the range of 0.1-200 mm,such as 0.2-200 mm, like especially 0.25-50 mm, such as 0.5-50 mm. Whena blue light source is applied, especially the luminescent materialabsorbs in the blue. Or, the other way around, when the luminescentmaterial absorbs in the blue, especially a light source may be appliedthat emits in the blue. In specific embodiments, the concentration ofthe luminescent material is chosen such that at least 90% of light inthe blue is absorbed within the first length (x) from the side face,wherein x/r≤0.4 applies, and wherein the first length (x) is equal to orless than 5 mm. In specific embodiments, x/r≤0.3, such as x/r≤0.2.However, especially, x/r≥0.01, such as x/r≥0.02.

Here, especially at least the side face may be irradiated by the lightsource.

As indicated above, the side face comprises a curvature with a radius(r). When the body comprises a plurality of side faces, such as in thecase of a body having a rectangular with one face being curved, at leastthe curved side face may be irradiated with the light source. One ormore side faces may comprise a radius, which may be different or whichmay be alike; especially they may be the same. The radius is especiallydefined in relation to a body axis. Further, a side face may comprise aplurality of curvature. In general, however, the number of differentcurvatures for a single side face are limited, or the radii are foundwithin a limited range (such as differing from each other within about5% from a mean value), or there is only a single radius value.

In specific embodiments, the side face has a convex shape. Further,especially a plurality of convex shaped side face may be available. Inyet other embodiments, however, there is essentially a single side facethat has a curvature. This is especially the case when a rod is appliedhaving a circular cross-section.

In embodiments the elongated body of the luminescent element especiallycomprises a first side face and a second side face, one of these beingconvex and one of these being concave, with the latter defining acavity. For instance, this may be the case when a concave shaped orconvex shape body is applied, by which one a convex and a concave sideface may in embodiments be available. Especially, in embodiments theelongated light transmissive body may have a tubular shape having acavity surrounded by the elongated light transmissive body. For yet evenhigher outcoupling efficiencies, the cavity may be filled with (anothermaterial). Therefore, in embodiments at least part of the cavity,especially the entire cavity, comprises a light transmissive material,differing in composition from the composition of the material of theelongated light transmissive body. In specific embodiments, the lighttransmissive material in the cavity has an index of refraction equal toor lower than the light transmissive material of the light transmissivebody (but higher than air). An example of a suitable filling maycomprise one or more of MgF₂ or CaF₂, silicone, glass or transparentceramics like spinel, poly crystalline alumina or sapphire, YAG or amaterial similar to the first body material, but without the phosphor.The materials should be transparent, but could be amorphous,poly-crystalline or single crystalline.

In this way, a body may be obtained with a (virtual) outer shell with ahigh concentration of the luminescent material, and a core with a lowerconcentration of the luminescent material (including essentially noluminescent material). For instance, a cerium containing garnet may beprovided as tube, with a filling of essentially the same garnet, withoutcerium. Such body with a core-shell configuration of the luminescentmaterial, with a higher concentration luminescent material in the shelland a lower concentration (including zero) at the core may inembodiments have a distribution which is essentially defined by one ormore specific regions with a high concentration, but all regionsessentially having the same concentration, and one or more specificregions with a low concentration (including zero), but also all theseregions essentially having the same concentration. This might inembodiments be a kind of binary distribution. In other embodiments, thedistribution may have a gradation, with a gradual decrease from arelatively highly concentrated region to a relatively low concentration(including in embodiments zero).

In specific embodiments, the light transmissive material in the cavityhas a substantially equal index of refraction to the material of thelight transmissive body. This may allow a substantial absence ofscattering of light at the interface. Such system can be realized bye.g. co-extrusion of starting materials (such as green masses) with andwithout cerium, respectively that are co-sintered into a monolithiccomponent.

Hence, in embodiments the refractive index throughout the elongatedlight transmissive body may be essentially constant, but the activator(such as trivalent cerium) may essentially be present only in a shell,which is configured as radiation input face (which may also be indicatedas light entrance window or light entrance face).

The elongated body may be, as indicated above, tubular. However, theelongated body may also be massive, and may e.g. have an essentiallycircular cross-section. Therefore, in embodiments the elongated lighttransmissive body has an axis of elongation (BA) and a circularcross-section perpendicular to the axis of elongation (BA).

Here, especially the elongated light transmissive body has a first face(or “first end face”) and a second face (or “second end face”) defininga length (L) of the elongated light transmissive body; wherein the sideface comprises the radiation input face, wherein the second facecomprises the radiation exit window.

Assuming e.g. solid round elongated light transmissive bodies, lightthat is generated in the “skin” of the rod may be carried by theelongated light transmissive body acting as a kind of light guide. Thelight that is aligned with the main axis (“body axis” or “axis ofelongation”) or under small angles with the main axis is coupled out viathe CPC. There is also a large portion of the light that moves along thecircumference of the rod with only a small component along the mainaxis, so these rays follow a kind of a screw pattern. When these raysare coupled out by the CPC the rays are under a very large angle withthe axial (z-)direction and add a lot to the value of the etendue.However, low values of the etendue are essential for a good performanceof the module. In case of an n_CPC_<n_rod, a lot of the light in the rodcannot escape from the rod via the side (non-TIR) or via the outer ends(TIR-to-Nose), but this light is “locked-in”. Reflections on the side oron the flat surface at the tail or the CPC do not change this propertyof the locked-in rays. Scattering (volume scattering or surfacescattering) can change the direction in such a way that locked-in rayscan either escape to the sides or to the CPC. In principle there-distribution of Locked-in light over these two routes by randomscattering is with weighing factors according to the solid angles ofnon-TIR light and TIR-to-Nose light. Therefore part of the locked-inlight is lost towards the side.

Hence, it is an aspect of the invention to provide an alternativelighting device comprising a luminescent concentrator, which preferablyfurther at least partly obviates one or more of above-describeddrawbacks and/or which may have a relatively higher efficiency. Thepresent invention may have as object to overcome or ameliorate at leastone of the disadvantages of the prior art, or to provide a usefulalternative.

It surprisingly appears that if one end or both ends of the rod arefaceted, the “screwing” rays are aligned better with the main axis afterreflection on one of the facets. By that the locked-in lightre-distribution is no longer ‘randomly’ over non-TIR and TIR-to-Nose,but the TIR-to-Nose fraction is increased and by that the efficiency ofthe module improves. Also the etendue of the output light is improved.However, at the same time the light that was heading axially towards themirror is affected. If the tilts of the facets are too big the facetingmay have a net negative effect on the total performance, so small anglesare required leading to top angles of at least about 100°, such as atleast about 120°, for example 170° top angles on the kink between thefacets. Further, it surprisingly appears that for placement of a mirrorat one outer end of the rod it can be useful to make the count as low aspossible, which could be just four facets. If reducing the facet counteven more, the effect of the facets is changed and the gain inperformance is less. A single facet on the rod end is an extreme case,which means the rod end is non-perpendicular to the side, it is tilted.This enables easy fixation of a mirror, but appears to be lesseffective. At the nose end (end with exit window) of the rod, a facetedstructure on the rod is also useful if the CPC has a lower refractiveindex than the rod. In embodiments, the CPC can be shaped with the samefacets to have a thin adhesive layer in between. Locked-in light canbounce up and down the rod and with each reflection at one of the outerends the light direction is aligned more with the z-axis. For a hollowor solid, round or elliptical rod similar facets are possible, ingeneral it makes sense to have the facets more at the edges and less inthe center of the rod ends. The same solution can be applied for arectangular rod, facets that merge/vanish in the rod center. It alsoappears to apply to solid rectangular rods and hollow rectangular rods.Therefore, in embodiments the CPC is especially shaped with the samefacets to match with the shape of the elongated light transmissive body.The CPC may thus be directly attached to the light transmissive body ormay be bonded to it by a thin adhesive layer in between. Alternatively,the CPC has a circumferential shape that differs from the elongatedlight transmissive body, which may be advantageous in specificapplications. Hence, using—in embodiments—facets at one or more ends ofan elongated light transmissive body having a circular cross-section ornon-circular cross-section (or non-tubular cross-section) appears to beadvantageous.

Hence, in an aspect the invention provides luminescent elementcomprising an elongated light transmissive body, the elongated lighttransmissive body comprising a side face, wherein: (i) the elongatedlight transmissive body comprises a luminescent material configured toconvert at least part of a light source light selected from one or moreof the UV, visible light, and IR received by the elongated lighttransmissive body into luminescent material radiation; (ii) theelongated light transmissive body has a first face and a second facedefining a length (L) of the elongated light transmissive body; and(iii) one or more of the first face and the second face comprise a planecomprising surface modulations thereby creating different modulationangles (β) relative to the respective plane.

As indicated above, such luminescent element may allow an increasedoutcoupling of the light from the elongated light transmissive body.Especially, the plane has at least two surface modulations, e.g. awedge-shaped first face or second face. Even more especially, the planehas at least four surface modulations, such as a tetragonal pyramidshaped first face or second face. However, with e.g. four surfacemodulations, also a kind of checker board structure or saddle shapestructure can be provided, with two faces forming a top and two facesforming a cavity. However, many more shapes are possible, includingmulti-faceted shapes and curved shapes. Further, the first face or thesecond face may have a cross-sectional shape selected from e.g. square,rectangular, round, oval, ring-like, etc. etc., which further adds tothe different options for creating modulations (see further also below).

In specific embodiments, the plane comprises n/cm² facets asmodulations, wherein n is selected from the range of 1-10,000, such as1-1000. Especially, at least two facets have different modulation angles(β). Hence, there may be two or more subsets having mutually differingmodulation angles but wherein within the subsets the modulation anglesmay be identical.

However, it appears that in some embodiments at least four facets mayalready improve the outcoupling and/or beam shape; a substantialincrease in gain was found. For round rods, one facet might work, but insimulations it appeared that at least four facets may have a desirableimpact on the outcoupling and/or beam shape. For round rods, i.e. forcylindrical shaped bodies, the facets are especially radiallyorientated. For rectangular, rods even a single facet may provide apositive effect on the gain, especially at least two, such as at leastfour.

In specific embodiments, especially when curved modulations are applied,the plane may comprise at least four different modulation angles (β).

Further, it appears that when the elongated light transmissive body hasa cross-section that include curves, such as having a roundcross-section (circular rod), the modulations are especially parallel tothe radii and are not configured with angles relative to the radii. Inother words, the modulations may be radially oriented and have—inspecific embodiments—essentially no radial deviations; especially thismay be realized when a substantial number of facets is applied, like atleast 10. When a limited number of facets is applied, such as four (ormore) facets, there may be some radial deviation of the facets.Therefore, in specific embodiments the elongated light transmissive bodyhas an axis of elongation (BA), the side face comprises a curvature witha radius (r); and the modulations have angles (γ) relative toperpendiculars (r1) to the axis of elongation (BA) selected from therange of 0-90°, such as 0-80°, such as 0-45°, like especially 0-35°,like in embodiments 0-20°, such as e.g. 0-10°, such as about 0°±5°, like0°±2°. Especially, the angles (γ) are >0°. Angles in the order of 25-35°seem beneficial for facets at the first face, optionally combined with areflector downstream thereof. Facets at the second face may have evenlarger mutual angles.

Especially, the term “facet” refers to a flat facet. In specificembodiments, the facets may be curved. For instance, when applying alimited number of facets, such as about four, at the first or secondsurface a body having a circular cross-sectional shape, in embodimentssuch facets may be curved.

Here, especially the elongated light transmissive body has a first faceand a second face defining a length (L) of the elongated lighttransmissive body; wherein the side face comprises the radiation inputface, wherein the second face comprises the radiation exit window.

For LED based projection, the first generation of High Lumen Densitymodules has been developed based on a luminescent concentrating rod thathas a rectangular cross section. This shape was chosen as it isconvenient to couple light into the rod and to cool the rod, while italso can be chosen to match with the aspect ratio of panels that areused for projection. There is however a strong desire for lower costsolutions, for other dimensions, for other shapes, for spectral tuningoptions, and for more robust module architectures.

Traditionally single crystal boules are drawn from a melt (Czochralskymethod) from which individual rods, e.g. for light conversion, arecreated by wire sawing, grinding and polishing. Typically square orrectangular rods are produced in this way, as also used in the firstgenerations of the High Lumen Density (HLD) light sources for projectionengines. New production technologies enable new cross-sectional shapes:via the micro pull down technology, almost any cross-section shape of asingle crystal linear structure can be created. For poly crystalmaterial via extrusion various shapes may be created, but then mostlikely additional polishing steps are required for light concentratorstructures. It appeared possible to manufacture diverse cross-sectionalshapes of single crystal material.

A suitable luminescent concentrator may be based on an elongated bodywith a plurality of light sources pumping the rod from the side, withthe rod having a rectangular cross-section.

With such configurations there may be some issues that may not be alwaysdesirable:

-   1. The luminescent rods can e.g. be manufactured from a large single    crystal by sawing with subsequent grinding and polishing, resulting    in very high process cost;-   2. Light losses are relatively high due to the four escape cones    associated with the four sides of the rods;-   3. Other applications do require other shapes of the light emitting    surface area of the light source, as there are e.g. the preferences    for circular beams in case of spot lamps, for efficient coupling    into (round) optical fibers (e.g. for microscope illumination), or    for content addition to illumination (by additional projection of    images);-   4. Positioning of the rectangular rod is difficult as it needs to be    mounted at a very small distance from the pump LEDs to achieve    reasonably high coupling efficiencies;-   5. As the highest pump LED brightness can be achieved by an array of    multiple chip-scale-package LEDs, and these dies all show side    emission next to top emission, there is an intrinsic penalty in    coupling efficiency due to relative high losses in the sidewards    emitted light;-   6. Application of spectrally different converters to tune the    overall light source spectrum is very elaborate due to practical    issues concerning placement of the converters.

This alternative single crystal manufacturing approach as describedbefore may offer a production technology where surface grinding andpolishing would not be needed anymore, enabling completely new shapesfor luminescent concentrating bodies that are out of reach forpolycrystalline converters.

Hence, it is an aspect of the invention to provide an alternativelighting device comprising a luminescent concentrator, which preferablyfurther at least partly obviates one or more of above-describeddrawbacks and/or which may have a relatively higher efficiency. Thepresent invention may have as object to overcome or ameliorate at leastone of the disadvantages of the prior art, or to provide a usefulalternative.

With the new converter shapes and module architectures as now presented,most or all of these disadvantages may be overcome or may besignificantly reduced, resulting in high brightness light sources withhighly reduced cost or with highly improved performance characteristics.Amongst others, a luminescent concentrating body with a specificcross-sectional shape that enables improved coupling efficiency,improved light extraction, improved cooling, improved convertermounting, improved module assembly, and/or improved light sourcerobustness by features related to that specific cross-sectional shape isherein proposed. Amongst others, one or more of the following featuresof an elongated light transmissive body and/or lighting device with suchbody may be included:

embedding of the pump LEDs and/or laser diodes within linear cavity inthe converter (and thereby improving the coupling efficiency of pumplight to the luminescent converter);

positioning/alignment of the converter body in the high brightnessmodule;

defining the distance from pump LEDs and/or laser diodes to theconverter (such as for an optimized coupling efficiency of pump lightinto the luminescent converter and/or for optimizing thermal transferfrom the luminescent converter via the LEDs of LDs to a heat sink;

reducing the light extraction cones from 4 down to 2 resulting inreduced light losses and therefore an increase module performance;

mounting of multiple converters next to each other or within each other,enabling spectral tuning of the light source output;

alignment of the pump LEDs or pump LDs relative to the luminescentconverter;

(control of) transfer of heat from the luminescent converter to thesubstrates of the pump LEDs or pump LDs;

(control of) transfer of heat from the luminescent converter via thepump LEDs or pump LDs to the heat sink by ensuring thermal contactbetween these components.

Specific converter cross sectional profiles that enable one or moredistinct advantages are I shapes, O shapes, T shapes, U shapes, and morecomplex versions can be provided with this solution.

Specific configurations combining LED and/or laser pumped converteremission with laser emission are enabled by some architectures with ahollow converter and covered by the scope of this invention.

In an aspect, the invention provides a luminescent element comprising anelongated light transmissive body, the elongated light transmissive bodycomprising a side face, wherein: (i) the elongated light transmissivebody comprises a luminescent material configured to convert at leastpart of a light source light selected from one or more of the UV,visible light, and IR received by the elongated light transmissive bodyinto luminescent material radiation; and (ii) the side face comprise acavity or a protrusion.

Such elongated element allows arrangement of other elements in thecavity and/or allows a functional coupling with yet other elements.

Therefore, in embodiments the elongated light transmissive body (of alighting device) comprises a cavity, and one or more light sources areat least partly configured in the cavity.

In yet other embodiments, the elongated light transmissive body (of alighting device) comprises a protrusion, wherein the lighting devicefurther comprises receptor element configured to host at least part ofthe protrusion. The receptor element can be a holder. In otherembodiments, the receptor element may be a heat sink (which may thus inembodiments also be configured as holder) of may be (thermally) coupledto a heat sink. Therefore, the receptor element can host at least partof the protrusion for alignment of the elongated light transmissive bodyand/or thermal energy transfer from the elongated light transmissivebody to the receptor element.

Likewise, the elongated light transmissive body (of a lighting device)comprises a cavity, wherein the lighting device further comprisesprotruding element configured to enter at least part of the cavity. Theprotruding element can be a holder. The protruding element can be aholder. In other embodiments, the protruding element may be a heat sink(which may thus in embodiments also be configured as holder) of may be(thermally) coupled to a heat sink. Therefore, the protruding elementcan at least partly be hosted in the cavity for alignment of theelongated light transmissive body and/or thermal energy transfer fromthe elongated light transmissive body to the protruding element.

Therefore, in embodiments the light sources may be configured at one ormore substrates, wherein the one or more substrates are configured asheat sinks or are thermally coupled with heat sinks. Alternatively oradditionally, in embodiments one or more reflectors may be configured atone or more substrates, wherein the one or more substrates areconfigured as heat sinks or are thermally coupled with heat sinks. Theuse of cavities and protrusions allow a combination of features, whichreduces space and which may also reduce undesired optical contact withthe body.

In embodiments, the elongated light transmissive body has across-sectional shape selected from the group consisting of an ovalshape (or O-shape), a U-shape, a T-shape, an I-shape and an H-shape,such as in embodiments a T-shape, an I-shape and an H-shape. In yetother embodiments, the elongated light transmissive body has an axis ofelongation (BA), and the elongated light transmissive body has across-sectional shape perpendicular to the axis of elongation (BA)selected from the group consisting an oval shape and a U-shape. The ovalshape may thus be hollow. The term “shape” especially refers to across-sectional shape. For irradiation an oval body with radiation,especially those part(s) of the side face(s) may be applied with thelarger radii.

In embodiments, the cavity may have a width of at least 0.2 mm, such asat least 0.5 mm, and a depth of at least 0.02 mm, such as at least 0.1mm, and a length of at least 1 mm, such as at least 5 mm. The cavitydimensions may have a volume selected from the range of about 0.1-10mm³. Such cavities can e.g. host a LED, or a plurality of LEDs.

The cavity can e.g. be configured as a trench, for hosting a pluralityof light sources. Hence, in embodiments the elongated light transmissivebody comprises one or more of a (i) a plurality of cavities, (ii) one ormore elongated cavities, (iii) a plurality of protrusions, and (iv) oneor more elongated protrusions.

The cavity may be used for one or more of (1) aligning the pump lightsources during mounting (on their substrate), (2) for having the pumplight sources in thermal contact (via their top surface) with the bodyto have the body cooled via the light sources, such as LEDs or LDs, and(3) enabling direct thermal contact between the elongated lighttransmissive body and the substrate or heat sink carrying the LEDs (orLDs) to enable heat transfer from the elongated light transmissive bodyto a heat sink.

In embodiments, the elongated light transmissive body may taper over atleast part of its length. Especially, the radiation exit window is at apart that tapers. In specific embodiments, a side face is slantedrelative to an end face. Note that a fully tapering may lead to avariant wherein a side face and an end face are essentially identical,such as in the case of a cone or in the case of a pyramid.

In specific embodiments, it appears beneficial when the tapering is suchthat the cross-sectional plane through which light may propagateessentially stays constant over the tapering. Such situation may beachieved when using a hollow body, wherein the tapering of an outerplane may be less than the tapering of an internal plane (of thecavity). Hence, in embodiments, the elongated light transmissive bodieshas a tubular cross-section perpendicular to an axis of elongation (BA),wherein the tubular elongated light transmissive body tapers along atleast part of the length of the axis of elongation (BA) whilemaintaining a cross-sectional area perpendicular to the axes ofelongation (BA) constant. In yet other embodiments, however, thecross-sectional area may reduce with (increasing) tapering, for instancewith a reduction of up to 20% (i.e. 80% of the cross-sectional area atthe broadest or untampered part), as recycling may further improve thegain. In yet further embodiments, the cross-section area may evenfurther reduce with (increasing) tapering.

In further specific embodiments, it may be beneficial when the taperingis such that the product of (i) the area of cross-sectional planethrough which the light is propagating and (b) the divergence of thepropagating light stays essentially constant over the tapering. Suchsituation may in embodiments be achieved when a CPC-like or other curvedwall shapes are applied in the tapering section. The divergence may e.g.be described as the solid angle (expressed in steradian) comprising thelight rays in the material.

When a body is used wherein the absorption is essentially in the skin,at an end face of the body light may escape in a way that reflects theabsorption. For instance, assuming a rod wherein light is essentiallyabsorbed in an outer ring, at an end face a ring like intensitydistribution will be generated. Hence, one may reflect the light at theradiation exit window with low intensity by arranging a reflector at theradiation exit window such that only part of the light can escape. Forinstance, in this way one can discriminate between areas that have lessthan 5%, or even less than 10% of the high intensity areas.

Therefore, in embodiments the luminescent element further comprising afirst reflector and a second reflector wherein:

the elongated light transmissive body has a first face and a second facedefining a length (L) of the elongated light transmissive body; whereinthe second face comprises a first radiation exit window;

the first reflector is configured at the first face and is configured toreflect radiation back into the elongated light transmissive body; and

the second reflector has a cross-section smaller than the radiation exitwindow, wherein the second reflector is configured to reflect radiationback into the light transmissive body.

As indicated above, the elongated light transmissive body may have e.g.a round cross-section, may be tubular, may have a rectangularcross-section, etc. In specific embodiments, the elongated lighttransmissive body may have a polygonal cross-section perpendicular tothe axes of elongation (BA). Especially, polygons with at least eightfaces, such as at least 10 faces, may also provide good efficiencies(when pumped with light source light). When more than one elongatedlight transmissive body is applied, one or more of the elongated lighttransmissive bodies may have polygonal cross-sections perpendicular tothe axes of elongation (BA). Hence, in alternative embodiments, theelongated light transmissive body, or the one or more of the elongatedlight transmissive bodies have circular cross-sections perpendicular tothe axes of elongation (BA). In further embodiments, the elongated lighttransmissive body, or the one or more of the elongated lighttransmissive bodies have tubular cross-sections perpendicular to theaxes of elongation (BA).

Further, in variants, the elongated light transmissive body, or the oneor more of the elongated light transmissive bodies taper along at leastpart of the length of the axes of elongation (BA). As indicated above,in such variants the elongated light transmissive body, or the one ormore of the elongated light transmissive bodies may have tubularcross-sections perpendicular to the axes of elongation (BA), wherein theone or more tubular elongated light transmissive bodies taper along atleast part of the length of the axes of elongation (BA) whilemaintaining a cross-sectional area perpendicular to the axes ofelongation (BA) constant.

If a solid cylinder is tapered, the cross-sectional area is changing(e.g., it reduces along the body axis over at least part of its length).As a consequence, the solid angle of the light rays changes as well(i.e.: it increases when the cross-sectional area decreases). For anarrowing tapering tube, if the wall thickness stays constant, the solidangle of the light rays increases, because the surface area throughwhich the rays propagate decreases. This is a consequence of the factthat surface area times the solid angle is at best constant, orincreases. If that surface area is kept constant, this may thus implythat the wall thickness increases. In such instance, the solid angle maystay constant. If solid angle times the surface area is constant, thenthe étendue may essentially be preserved(=constant), which is in manyembodiments desired. Therefore, in embodiment the invention alsoprovides configurations wherein the surface area times the solid angleis essentially constant. This may also refer to configurations in whichthe surface area increases during the tapering.

The term “tubular” may especially refer to an element having a curvedcross-section, especially round. However, the term “tubular” may also beused for tubes having a rectangular or polygonal cross-section. Unlessindicated otherwise, it is assumed that the cross-section of the cavity(of the tube) has essentially the same symmetry as the cross-section ofthe walls of the tube.

In embodiments, the body and the optical element may comprise identicalmaterials and only slightly differ in composition. For instance, inembodiments the body comprises a cerium doped garnet and the opticalelement comprises the same garnet essentially without cerium. Therefore,in embodiments the elongated light transmissive body comprises a firstmaterial having a first composition, and the optical element comprises asecond material having a second composition, and wherein the firstcomposition and the second composition comprise identical materials.Note that in embodiments the optical element may also compriseluminescent material.

In specific embodiments, the elongated light transmissive body and theoptical element are a single crystalline or a poly crystalline ceramicbody. Such single body may be produced with the process as describedherein.

In such embodiments, one may desire to have a higher concentration ofluminescent material in the body than in the optical element; the lattere.g. having no luminescent material. Therefore, in embodiments theelongated light transmissive body comprises the luminescent materialwith a first concentration c1, and the optical element optionallycomprises the luminescent material with a second concentration c2,wherein 0≤c2/c≤1, such as 0≤c2/c≤0.1, like 0≤c2/c1≤0.01. In embodiments,wherein the host material stays the same, and only the activatorconcentration changes, the terms “first concentration” and “secondconcentration”, and where applicable similar terms, may refer to aconcentration of the activator.

As indicated above, in specific embodiments the optical elementcomprises a compound parabolic concentrator or an adapted compoundparabolic concentrator.

In yet further embodiments, the optical element comprises a hollowoptical element. In yet further embodiments, the optical elementcomprises a massive body. The former may especially be for at least beamshaping, the latter may especially be for at least (further)facilitating light extraction from the elongated light transmissivebody.

Hence, in specific embodiments the optical element comprises a solidbody for facilitating outcoupling of light from the elongated lighttransmissive body, and the optical element and the elongated lighttransmissive body are configured in optical contact with each other.

The lighting device as described herein may thus further comprise anoptical element. The optical element may optically be coupled with thefirst radiation exit window (of the elongated light transmissive body).The optical element may comprise a radiation entrance window configuredto receive at least part of the converter radiation and a radiation exitwindow for escape from beam shaped converter radiation from the opticalelement. Further, the optical element may in embodiments also allowescape from the optical element with a higher efficiency than from theelongated light transmissive body in absence of the optical element, asthe optical element may facilitate light extraction from the elongatedlight transmissive body. Light extraction may amongst others befacilitated with matching refractive indices. The closer to therefractive indices are, the better the extraction. Further, the smallerthe deviation from the normal to that emission surface, the lower theFresnel reflections and therefor the higher the extraction. The presenceof an AR (anti-reflex) coating, such as on the light emission window,may also be beneficial.

Assuming the optical element also to be a body, such body is thus lighttransmissive, and may comprises materials as indicated elsewhere herein,especially in embodiments a material that is similar to the material ofthe elongated body. The refractive index thereof may be indicated assecond refractive index n2; the refractive index of the material of theelongated light transmissive body may be indicated as first refractiveindex. At one or more (relevant) wavelengths, e.g. in the visible, suchas at e.g. 550 nm, the second refractive index is in the range of60-140%, such as especially in the range of 70-130% of the refractiveindex of the first material. When primarily (N)UV or (N)IR is to becoupled out, this may apply to a (N)UV or (N)IR wavelength,respectively.

Hence, in embodiments the lighting device may further comprise anoptical element, wherein the optical element is configured to one ormore of (i) collimating the luminescent radiation and (ii) extractingluminescent radiation from the elongated light transmissive body.Further, the optical element may be (a) optically coupled to theelongated light transmissive body, or the optical element and theelongated light transmissive body may be comprised by a single body(optionally also including an intermediate mixing element).

The term “luminescent element” is applied, as under irradiation with oneor more of UV and visible light, the luminescent material willluminesce, whereby the transmissive body provides luminescent materialradiation or converter radiation. Hence, the luminescent material isconfigured to convert at least part of a light source light selectedfrom one or more of the UV, visible light, and IR received by theelongated light transmissive body into luminescent material radiation.

The luminescent element may have different shapes, which will beelucidated below, but in general has at least a side face and anotherface (in embodiments also indicated as “first face”). The side face, oryet another face may especially be configured as radiation exit windowor may comprise such radiation exit window. The first face mayespecially be configured as back face, e.g. with a mirror configureddownstream thereof. Hence, especially, the light source will irradiateone or more of the first face and the side face. Especially, inembodiments the radiation exit face and the side face are configuredrelative to each other under an angle being larger than 0° and beingsmaller than 180°, such as 90°. Further, especially, the first face andthe side face are configured relative to each other under an angle beinglarger than 0° and being smaller than 180°, such as 90°. The first faceand the radiation exit face may be configured parallel, though inspecific embodiment the radiation exit face may be configured slantedrelative to the first face. The first face and the second face maydefine a (largest) length of the elongated body. The elongated lighttransmissive body comprises a body axis, which may also be indicated asaxis of elongation. Embodiments like these, and further embodiments, aredefined in more detail below. The second face may comprise the radiationexit window. The radiation exit window may also be indicated as “lightextraction window”.

Note that the light transmissive body is transmissive for light but maybe absorbing for other light. Especially, the light transmissive bodyabsorbs at least part of one or more of excitation radiation, such as UVand blue radiation (or other radiation). However, especially the lighttransmissive body has a low absorption (and a low scattering), and thushigh transmission, for emission radiation, such as in the green and/oryellow (or other emission wavelengths larger than excitation radiation.

For instance, when a UV light source is applied, the light transmissivebody may be transmissive for blue light. Hence, especially the lighttransmissive body has a relatively high absorption for one or morewavelengths in the range where the luminescent material absorbs lightand a substantially lower absorption, such as at least 10 times less,for one or more wavelengths where the luminescent material emits light(in the visible).

For elongated light transmissive bodies that have a curved side face, itmay be desirable that the light of the light source is essentiallyabsorbed in the “skin” of the light transmissive body. However, not onlyfor curved faces it may be desirable to absorb essentially all lightclose to the surface. Also, for elongated light transmissive bodies thathave a polygonal cross-section this may be advantageous, such as forbodies with non-rectangular cross-sections, such as a hexagonal oroctagonal cross-section. Such light transmissive bodies may have athickness d, and may have a concentration of the luminescent materialchosen such that at least 80% of light at one or more radiationwavelengths is absorbed within a first length x from the side face,wherein 2*x/d≤0.4 applies, especially 2*x/d≤0.3, such as 2*x/d≤0.2.However, especially 2*x/d≥0.02.

Further, for instance to (further) influence the etendue (associatedwith the (minimum) total area comprising the elongated lighttransmissive body in a cross-sectional plane of the elongated lighttransmissive body), the elongated light transmissive body may taperalong at least part of the length of an axis of elongation (BA).Further, it also appears that applying a surface modulation to an endface and/or a light outcoupling face may increase the light outcoupling.For instance, the first face (an end face) may comprise surfacemodulations. Therefore, in specific embodiments one or more of the firstface and the second face may comprise a plane comprising surfacemodulations thereby creating different modulation angles (β) relative tothe respective plane.

Further, an optical element may be used to beam shape and/or facilitatelight extraction from the elongated light transmissive body. Therefore,in embodiments the luminescent element may further comprise an opticalelement optically coupled to the elongated light transmissive body. Inyet further specific embodiments, the elongated light transmissive bodyand the optical element are a single body. In such embodiments, theradiation exit window may effectively be configured at the opticalelement. The optical element may in embodiments be selected from thegroup consisting of a compound parabolic concentrator, an adaptedcompound parabolic concentrator, a dome, a wedge-shaped structure, aconical structure, etc.

Examples of the material(s) of the elongated light transmissive body areelucidated further below. In specific embodiments, the elongated lighttransmissive body is obtainable by a process comprising (a) one or moreof extrusion, injection molding, pressing, and casting, and (b)sintering.

Therefore, in yet a further aspect the invention provides a method forproducing an elongated light transmissive body, the method comprising(a) one or more of extruding, injection molding, pressing, and casting,a starting composition (b) sintering the thus obtained product.Especially, the product after sintering is further hot isostaticallypressed. In embodiments, this may include pre-forming of individualcomponents, followed by co-sintering of the components while being inphysical contact. In other embodiments, this may include forming thecomplete body in a single process step, e.g. by co-injection molding orco-extrusion, followed by a sintering process.

Such methods also allow tuning the concentration of the luminescentmaterial, such as an outer shell of the elongated body comprisingluminescent material (e.g. YAG with cerium), and a core comprisingessentially no luminescent material (e.g. YAG essentially withoutcerium). Such methods also allow integration of the optical element andthe elongated light transmissive body. In such methods, it may also bepossible to create the elongated light transmissive body withluminescent material, and the optical element without luminescentmaterial. After sintering or before sintering, especially aftersintering, isostatic pressure may be applied. Therefore, in embodimentsthe process may further comprises (c) isostatic pressing.

Assuming cerium as dopant, the average concentration of the dopant inthe elongated light transmissive body may be selected from the range of0.01-2 mole %, such as 0.01-1.5 mole %, such as 0.03-0.9 mole %.

As indicated above, the body may have a skin with luminescent materialand a core with no or a lower concentration of luminescent material.Therefore, in embodiments a first composition comprising the luminescentmaterial with a first concentration cl, and a second compositionoptionally comprises the luminescent material with a secondconcentration c2, wherein 0≤c2/c≤1, are applied, to provide theelongated light transmissive body having a higher concentration of theluminescent material at the side face than further away from the sideface.

In yet a further aspect, the invention also provides a lighting devicecomprising:

a light source configured to provide light source light;

the luminescent element as defined herein, wherein the elongated lighttransmissive body comprises a radiation input face and a first radiationexit window; wherein the luminescent material is configured to convertat least part of light source light received at the radiation input faceinto luminescent material radiation, and the luminescent elementconfigured to couple at least part of the luminescent material radiationout at the first radiation exit window as converter radiation.

In embodiments of the lighting device, the lighting device may comprisea plurality of bodies. In embodiments, different light sources areconfigured to irradiate different bodies. In this way, intensity of thelighting device light may be controlled. Would the bodies includedifferent luminescent materials (or optionally different concentrationsof the same luminescent material) then also the spectral distribution ofthe lighting device light may be controlled. Hence, the lighting devicemay further comprise a control system configured to control the lightsources (and thereby one or more optical properties of the lightingdevice light). The plurality of bodies may include a monolithicconfiguration, wherein the bodies are essentially inseparable, such asobtained with e.g. co-extrusion. The plurality of bodies may alsoinclude a core-shell configuration wherein the core and shell haveessentially no physical contact, like a (smaller) cylinder in a tube.The plurality of bodies may also include essentially separated bodies,which are e.g. configured parallel to each other, or are configured inan array, with distances, e.g. at least larger than the wavelength(s) ofinterest between adjacent bodies.

In embodiment, the light of the different bodies may be bundled via asingle collimator or other optical element to provide the lightingdevice light.

A system may execute an action in a mode. The term “mode” may also beindicated as “controlling mode”. This does not exclude that the systemmay also be adapted for providing another controlling mode, or aplurality of other controlling modes. However, the control system isadapted to provide at least a controlling mode. Would other modes beavailable, the choice of such modes may especially be executed via auser interface, though other options, like executing a mode independence of a sensor signal or a (time) scheme may also be possible.

Hence, the lighting device may further comprise or may be functionallycoupled to a control system, configured to control the one or more lightsources of the lighting device.

The term “controlling” and similar terms especially refer at least todetermining the behavior or supervising the running of an element.Hence, herein “controlling” and similar terms may e.g. refer to imposingbehavior to the element (determining the behavior or supervising therunning of an element), etc., such as e.g. measuring, displaying,actuating, opening, shifting, changing temperature, etc. Beyond that,the term “controlling” and similar terms may additionally includemonitoring. Hence, the term “controlling” and similar terms may includeimposing behavior on an element and also imposing behavior on an elementand monitoring the element. In embodiments, one or more of the lightsources may be controlled by controlling the forward current and/or theduty cycle. Further, two or more (subsets of) light sources may becontrolled at different operation conditions (including differentoperation schemes).

As indicated above, the lighting device may comprise a plurality oflight sources to provide light source light that is at least partlyconverted by the light transmissive body, more especially theluminescent material of the light transmissive body, into converterradiation. The converted light can at least partially escape form thefirst radiation exit window, which is especially in optical contact withthe optical element, more especially the radiation entrance windowthereof.

The optical element may especially comprise a collimator used to convert(to “collimate”) the light beam into a beam having a desired angulardistribution. Further, the optical element especially comprises a lighttransmissive body comprising the radiation entrance window. Hence, theoptical element may be a body of light transmissive material that isconfigured to collimate the converter radiation from the luminescentbody.

In specific embodiments, the optical element comprises a compoundparabolic like collimator, such as a CPC (compound parabolicconcentrator).

A massive collimator, such as a massive CPC, may especially be used asextractor of light and to collimate the (emission) radiation.Alternatively, one may also configure a dome with optical contact(n>1.00) on the nose of the rod or a hollow collimator, such as a CPC,to concentrate the (emission) radiation.

The optical element may have cross section (perpendicular to an opticalaxis) with a shape that is the same as the cross-section of theluminescent body (perpendicular to the longest body axis (which bodyaxis is especially parallel to a radiation input face). For instance,would the latter have a rectangular cross section, the former may alsohave such rectangular cross section, though the dimension may bedifferent. Further, the dimension of the optical element may vary overits length (as it may have a beam shaping function).

Further, the shape of the cross-section of the optical element may varywith position along the optical axis. In a specific configuration, theaspect ratio of a rectangular cross-section may change, preferablymonotonically, with position along the optical axis. In anotherpreferred configuration, the shape of the cross-section of the opticalelement may change from round to rectangular, or vice versa, withposition along the optical axis.

As indicated above, first radiation exit window (of the elongated lighttransmissive body) is in optical contact with the radiation entrancewindow of the optical element. The term “optical contact” and similarterms, such as “optically coupled” especially mean that the lightescaping the first radiation exit window surface area (A1) may enter theoptical element radiation entrance window with minimal losses (such asFresnel reflection losses or TIR (total internal reflection) losses) dueto refractive index differences of these elements. The losses may beminimized by one or more of the following elements: a direct opticalcontact between the two optical elements, providing an optical gluebetween the two optical elements, preferably the optical glue having arefractive index higher that the lowest refractive index of the twoindividual optical elements, providing the two optical elements in closevicinity (e.g. at a distance much smaller than the wavelength of thelight), such that the light will tunnel through the material presentbetween the two optical elements, providing an optically transparentinterface material between the two optical elements, preferably theoptically transparent interface material having a refractive indexhigher that the lowest refractive index of the two individual opticalelements, the optically transparent interface material might be a liquidor a gel or providing optical Anti Reflection coatings on the surfacesof (one or both of) the two individual optical elements. In embodiments,the optically transparent interface material may also be a solidmaterial. Further, the optical interface material or glue especially mayhave a refractive index not higher than the highest refractive index ofthe two individual optical elements.

Instead of the term “in optical contact” also the terms “radiationallycoupled” or “radiatively coupled” may be used. The term “radiationallycoupled” especially means that the luminescent body (i.e. the elongatedlight transmissive body) and the optical element are associated witheach other so that at least part of the radiation emitted by theluminescent body is received by the luminescent material. Theluminescent body and the optical element, especially the indicated“windows” may in embodiments be in physical contact with each other ormay in other embodiments be separated from each other with a (thin)layer of optical glue, e.g. having a thickness of less than about 1 mm,preferably less than 100 μm. When no optically transparent interfacematerial is applied, the distance between two elements being in opticalcontact may especially be about at maximum the wavelength of relevance,such as the wavelength of an emission maximum. For visible wavelengths,this may be less than 1 μm, such as less than 0.7 μm, and for blue evensmaller.

Likewise, the light sources are radiationally coupled with theluminescent body, though in general the light sources are not inphysical contact with the luminescent body (see also below). As theluminescent body is a body and as in general also the optical element isa body, the term “window” herein may especially refer to side or a partof a side. Hence, the luminescent body comprises one or more side faces,wherein the optical element is configured to receive at the radiationentrance window at least part of the converter radiation that escapesfrom the one or more side faces.

This radiation may reach the entrance window via a gas, such as airdirectly. Additionally or alternatively, this radiation may reach theentrance window after one or more reflections, such as reflections at amirror positioned nearby the luminescent body. Hence, in embodiments thelighting device may further comprise a first reflective surface,especially configured parallel to one or more side faces, and configuredat a first distance from the luminescent body, wherein the firstreflective surface is configured to reflect at least part of theconverter radiation that escapes from the one or more side faces backinto the luminescent body or to the optical element. The space betweenthe reflective surface and the one or more side faces comprises a gas,wherein the gas comprises air. The first distance may e.g. be in therange of 0.1 μm-20 mm, such as in the range of 1 μm-10 mm, like 2 μm-10mm.

Especially, the distance is at least wavelength of interest, moreespecially at least twice the wavelength of interest. Further, as theremay be some contact, e.g. for holding purposes or for distance holderpurposes, especially an average distance is at least λ_(i), such as atleast 1.5*λ_(i), like at least 2*λ_(i), such as especially about5*λ_(i), wherein λ_(i) is the wavelength of interest. Especially,however, the average distance is in embodiments not larger than 50 μm,such as not larger than 25 μm, like not larger than 20 μm, like notlarger than 10 μm, for purposes of good thermal contact. Likewise, suchaverage minimum distance may apply to a reflector and/or optical filterconfigured at e.g. an end face, or other optical components as well.Optionally, in embodiments an element may comprise both heat sinkingfunction a reflection function, such as a heat sink with a reflectivesurface, or a reflector functionally coupled to a heat sink.

The lighting device may be configured to provide blue, green, yellow,orange, or red light, etc. Alternatively or additionally, inembodiments, the lighting device may (also) be configured to provide oneor more of UV, such as near UV (especially in the range of 320-400 nm),and IR, such as near IR (especially in the range of 750-3000 nm).Further, in specific embodiment, the lighting device may be configuredto provide white light. If desired, monochromaticity may be improvedusing optical filter(s). The definitions of near UV and near infraredmay partly overlap with the generally used definition for visible light,which is 380-780 nm.

The term “light concentrator” or “luminescent concentrator” is hereinused, as one or more light sources irradiate a relative large surface(area) of the light converter, and a lot of converter radiation mayescape from a relatively small area (exit window) of the lightconverter. Thereby, the specific configuration of the light converterprovides its light concentrator properties. Especially, the lightconcentrator may provide Stokes-shifted light, which is Stokes shiftedrelative to the pump radiation. Hence, the term “luminescentconcentrator” or “luminescent element” may refer to the same element,especially an elongated light transmissive body (comprising aluminescent material), wherein the term “concentrator” and similar termsmay refer to the use in combination with one or more light sources andthe term “element” may be used in combination with one or more,including a plurality, of light sources. When using a single lightsource, such light source may e.g. be a laser, especially a solid statelaser (like a LED laser). The elongated light transmissive bodycomprises a luminescent material and can herein especially be used asluminescent concentrator. The elongated light transmissive body isherein also indicated as “luminescent body”. Especially, a plurality oflight sources may be applied.

The terms “upstream” and “downstream” relate to an arrangement of itemsor features relative to the propagation of the light from a lightgenerating means (here the especially the light source(s)), whereinrelative to a first position within a beam of light from the lightgenerating means, a second position in the beam of light closer to thelight generating means is “upstream”, and a third position within thebeam of light further away from the light generating means is“downstream”.

The light concentrator comprises a light transmissive body. The lightconcentrator is especially described in relation to an elongated lighttransmissive body, such as a ceramic rod or a crystal, such as a singlecrystal. However, these aspects may also be relevant for other shapedceramic bodies or single crystals. In specific embodiments, theluminescent body comprises a ceramic body or single crystal.

The light transmissive body has light guiding or wave guidingproperties. Hence, the light transmissive body is herein also indicatedas waveguide or light guide. As the light transmissive body is used aslight concentrator, the light transmissive body is herein also indicatedas light concentrator. The light transmissive body will in general have(some) transmission of one or more of (N)UV, visible and (N)IRradiation, such as in embodiments at least visible light, in a directionperpendicular to the length of the light transmissive body. Without theactivator (dopant) such as trivalent cerium, the internal transmissionin the visible might be close to 100%.

The transmission of the light transmissive body for one or moreluminescence wavelengths may be at least 80%/cm, such as at least90%/cm, even more especially at least 95%/cm, such as at least 98%/cm,such as at least 99%/cm. This implies that e.g. a 1 cm³ cubic shapedpiece of light transmissive body, under perpendicular irradiation ofradiation having a selected luminescence wavelength (such as awavelength corresponding to an emission maximum of the luminescence ofthe luminescent material of the light transmissive body), will have atransmission of at least 95%.

Herein, values for transmission especially refer to transmission withouttaking into account Fresnel losses at interfaces (with e.g. air). Hence,the term “transmission” especially refers to the internal transmission.The internal transmission may e.g. be determined by measuring thetransmission of two or more bodies having a different width over whichthe transmission is measured. Then, based on such measurements thecontribution of Fresnel reflection losses and (consequently) theinternal transmission can be determined. Hence, especially, the valuesfor transmission indicated herein, disregard Fresnel losses.

In addition to a high transmission for the wavelength(s) of interest,also the scattering for the wavelength(s) may especially be low. Hence,the mean free path for the wavelength of interest only taking intoaccount scattering effects (thus not taking into account possibleabsorption (which should be low anyhow in view of the hightransmission), may be at least 0.5 times the length of the body, such asat least the length of the body, like at least twice the length of thebody. For instance, in embodiments the mean free path only taking intoaccount scattering effects may be at least 5 mm, such as at least 10 mm.The wavelength of interest may especially be the wavelength at maximumemission of the luminescence of the luminescent material. The term “meanfree path” is especially the average distance a ray will travel beforeexperiencing a scattering event that will change its propagationdirection.

The terms “light” and “radiation” are herein interchangeably used,unless clear from the context that the term “light” only refers tovisible light. The terms “light” and “radiation” may thus refer to UVradiation, visible light, and IR radiation. In specific embodiments,especially for lighting applications, the terms “light” and “radiation”refer to visible light.

The term UV radiation may in specific embodiments refer to near UVradiation (NUV). Therefore, herein also the term “(N)UV” is applied, torefer to in general UV, and in specific embodiments to NUV. The term IRradiation may in specific embodiments refer to near IR radiation (NIR).Therefore, herein also the term “(N)IR” is applied, to refer to ingeneral IR, and in specific embodiments to NIR.

Herein, the term “visible light” especially relates to light having awavelength selected from the range of 380-780 nm. The transmission canbe determined by providing light at a specific wavelength with a firstintensity to the light transmissive body under perpendicular radiationand relating the intensity of the light at that wavelength measuredafter transmission through the material, to the first intensity of thelight provided at that specific wavelength to the material (see alsoE-208 and E-406 of the CRC Handbook of Chemistry and Physics, 69thedition, 1088-1989).

The light transmissive body may have any shape, such as beam (or bar)like or rod like, however especially beam like (cuboid like). However,the light transmissive body may also be disk like, etc. The lighttransmissive body, such as the luminescent concentrator, might behollow, like a tube, or might be filled with another material, like atube filled with water or a tube filled with another solid lighttransmissive medium. The invention is not limited to specificembodiments of shapes, neither is the invention limited to embodimentswith a single exit window or outcoupling face. Below, some specificembodiments are described in more detail. Would the light transmissivebody have a circular cross-section, then the width and height may beequal (and may be defined as diameter). Especially, however, the lighttransmissive body has a cuboid like shape, such as a bar like shape, andis further configured to provide a single exit window.

In a specific embodiment, the light transmissive body may especiallyhave an aspect ratio larger than 1, i.e. the length is larger than thewidth. In general, the light transmissive body is a rod, or bar (beam),or a rectangular plate, though the light transmissive body does notnecessarily have a square, rectangular or round cross-section. Ingeneral, the light source is configured to irradiate one (or more) ofthe longer faces (side edge), herein indicated as radiation input face,and radiation escapes from a face at a front (front edge), hereinindicated as radiation exit window. The light source(s) may provideradiation to one or more side faces, and optionally an end face. Hence,there may be more than one radiation input face.

Especially, in embodiments the solid state light source, or other lightsource, is not in (direct) physical contact with the light transmissivebody.

Physical contact (between the light exit window(s) of the lightsource(s) and the light entrance window(s) of the light transmissivebody/bodies) may lead to undesired outcoupling (from the lighttransmissive body) and thus a reduction in concentrator efficiency.Hence, especially there is substantially no physical contact. If theactual contact area is kept small enough, the optical impact may benegligible or at least acceptable. Therefore, it may be perfectlyacceptable to have some physical contact, e.g. by some small points asresulting from a certain surface roughness, or non-perfectly flatsurface, or by some intentionally created “highest spots” on a surfacethat will define a certain average distance between the two surfacesthat don't extract substantial amounts of light while enabling a shortaverage distance.

Further, in general the light transmissive body comprises twosubstantially parallel faces, a radiation input face and oppositethereof the opposite face. These two faces define herein the width ofthe light transmissive body. In general, the length of these facesdefines the length of the light transmissive body. However, as indicatedabove, and also below, the light transmissive body may have any shape,and may also include combinations of shapes. Especially, the radiationinput face has an radiation input face area (A), wherein the radiationexit window has a radiation exit window area (E), and wherein theradiation input face area (A) is at least 1.5 times, even moreespecially at least two times larger than the radiation exit window area(E), especially at least 5 times larger, such as in the range of2-50,000, especially 5-5,000 times larger. Hence, especially theelongated light transmissive body comprises a geometrical concentrationfactor, defined as the ratio of the area of the radiation input facesand the area of the radiation exit window, of at least 1.5, such as atleast 2, like at least 5, or much larger (see above). This allows e.g.the use of a plurality of solid state light sources (see also below).For typical applications like in automotive, digital projectors, or highbrightness spot light applications, a small but high radiant flux orluminous flux emissive surface is desired. This cannot be obtained witha single LED, but can be obtained with the present lighting device.Especially, the radiation exit window has a radiation exit window area(E) selected from the range of 1-100 mm². With such dimensions, theemissive surface can be small, whereas nevertheless high radiance orluminance may be achieved. As indicated above, the light transmissivebody in general has an aspect ratio (of length/width). This allows asmall radiation exit surface, but a large radiation input surface, e.g.irradiated with a plurality of solid state light sources. In a specificembodiment, the light transmissive body has a width (W) selected fromthe range of 0.5-100 mm, such as 0.5-10 mm. The light transmissive bodyis thus especially an integral body, having the herein indicated faces.

The generally rod shaped or bar shaped light transmissive body can haveany cross-sectional shape, but in embodiments has a cross section theshape of a square, rectangle, round, oval, triangle, pentagon, orhexagon. Generally the ceramic or crystal bodies are cuboid. In specificembodiments, the body may be provided with a different shape than acuboid, with the light input surface having somewhat the shape of atrapezoid. By doing so, the light flux may be even enhanced, which maybe advantageous for some applications. Hence, in some instances (seealso above) the term “width” may also refer to diameter, such as in thecase of a light transmissive body having a round cross section. Hence,in embodiments the elongated light transmissive body further has a width(W) and a height (H), with especially L>W and L>H. Especially, the firstface and the second face define the length, i.e. the distance betweenthese faces is the length of the elongated light transmissive body.These faces may especially be arranged parallel. Further, in a specificembodiment the length (L) is at least 2 cm, like 3-20 cm, such as 4-20cm, such as at maximum 15 cm. Other dimensions may, however, also bepossible, such as e.g. 0.5-2 cm.

Especially, the light transmissive body has a width (W) selected toabsorb more than 95% of the light source light. In embodiments, thelight transmissive body has a width (W) selected from the range of0.03-4 cm, especially 0.05-2 cm, such as 0.1-1.5 cm, like 0.1-1 cm. Withthe herein indicated cerium concentration, such width is enough toabsorb substantially all light (especially at the excitation wavelengthwith maximum excitation intensity) generated by the light sources.

The light transmissive body may also be a cylindrically shaped rod. Inembodiments the cylindrically shaped rod has one flattened surface alongthe longitudinal direction of the rod and at which the light sources maybe positioned for efficient incoupling of light emitted by the lightsources into the light transmissive body. The flattened surface may alsobe used for placing heatsinks. The cylindrical light transmissive bodymay also have two flattened surfaces, for example located opposite toeach other or positioned perpendicular to each other. In embodiments theflattened surface extends along a part of the longitudinal direction ofthe cylindrical rod. Especially however, the edges are planar andconfigured perpendicular to each other.

The side face is especially such flattened surface(s). The flattenedsurface especially has a relatively low surface roughness, such as an Raof at maximum 100 nm, such as in the range of 5-100 nm, like up to 50nm.

The light transmissive body may also be a fiber or a multitude offibers, for instance a fiber bundle, either closely spaced or opticallyconnected in a transparent material. The fiber may be referred to as aluminescent fiber. The individual fiber may be very thin in diameter,for instance, 0.1 to 0.5 mm. The light transmissive body may alsocomprise a tube or a plurality of tubes. In embodiments, the tube (ortubes) may be filled with a gas, like air or another gas having higherheat conductivity, such as helium or hydrogen, or a gas comprising twoor more of helium, hydrogen, nitrogen, oxygen and carbon dioxide. Inembodiments, the tube (or tubes) may be filled with a liquid, such aswater or (another) cooling liquid.

The light transmissive body as set forth below in embodiments accordingto the invention may also be folded, bended and/or shaped in the lengthdirection such that the light transmissive body is not a straight,linear bar or rod, but may comprise, for example, a rounded corner inthe form of a 90 or 180 degrees bend, a U-shape, a circular orelliptical shape, a loop or a 3-dimensional spiral shape having multipleloops. This provides for a compact light transmissive body of which thetotal length, along which generally the light is guided, is relativelylarge, leading to a relatively high lumen output, but can at the sametime be arranged into a relatively small space. For example, luminescentparts of the light transmissive body may be rigid while transparentparts of the light transmissive body are flexible to provide for theshaping of the light transmissive body along its length direction. Thelight sources may be placed anywhere along the length of the folded,bended and/or shaped light transmissive body.

Parts of the light transmissive body that are not used as lightincoupling area or light exit window may be provided with a reflector.Hence, in an embodiment the lighting device further comprises areflector configured to reflect luminescent material radiation back intothe light transmissive body. Therefore, the lighting device may furtherinclude one or more reflectors, especially configured to reflectradiation back into the light transmissive body that escapes from one ormore other faces than the radiation exit window. Especially, a faceopposite of the radiation exit window may include such reflector, thoughin an embodiment not in physical contact therewith. Hence, thereflectors may especially not be in physical contact with the lighttransmissive body. Therefore, in an embodiment the lighting devicefurther comprises an optical reflector (at least) configured downstreamof the first face and configured to reflect light back into theelongated light transmissive body. Alternatively or additionally,optical reflectors may also be arranged at other faces and/or parts offaces that are not used to couple light source light in or luminescencelight out. Especially, such optical reflectors may not be in physicalcontact with the light transmissive body. Further, such opticalreflector(s) may be configured to reflect one or more of theluminescence and light source light back into the light transmissivebody. Hence, substantially all light source light may be reserved forconversion by the luminescent material (i.e. the activator element(s)such as especially Ce³⁺) and a substantial part of the luminescence maybe reserved for outcoupling from the radiation exit window. The term“reflector” may also refer to a plurality of reflectors.

The one or more reflectors may consist of a metal reflector, such as athin metal plate or a reflective metal layer deposited on a substrate,such as e.g. glass. The one or more reflectors may consist of an opticaltransparent body containing optical structure to reflect (part) of thelight such as prismatic structures. The one or more reflectors mayconsist of specular reflectors. The one or more reflectors may containmicrostructures, such as prism structures or saw tooth structures,designed to reflect the light rays towards a desired direction.

Preferably, such reflectors are also present in the plane where thelight sources are positioned, such that that plane consist of a mirrorhaving openings, each opening having the same size as a correspondinglight source allowing the light of that corresponding light source topass the mirror layer and enter the elongated (first) light transmissivebody while light that traverses from the (first) light transmissive bodyin the direction of that plane receives a high probability to hit themirror layer and will be reflected by that mirror layer back towards the(first) light transmissive body.

The terms “coupling in” and similar terms and “coupling out” and similarterms indicate that light changes from medium (external from the lighttransmissive body into the light transmissive body, and vice versa,respectively). In general, the light exit window will be a face (or apart of a face), configured (substantially) perpendicular to one or moreother faces of the waveguide. In general, the light transmissive bodywill include one or more body axes (such as a length axis, a width axisor a height axis), with the exit window being configured (substantially)perpendicular to such axis. Hence, in general, the light input face(s)will be configured (substantially) perpendicular to the light exitwindow. Thus, the radiation exit window is especially configuredperpendicular to the one or more radiation input faces. Therefore,especially the face comprising the light exit window does not comprise alight input face.

For further improving efficiency and/or for improving the spectraldistribution several optical elements may be included like mirrors,optical filters, additional optics, etc.

In specific embodiments, the lighting device may have a mirrorconfigured at the first face configured to reflect light back into theelongated light transmissive body, and/or may have one or more of anoptical filter, a (wavelength selective) mirror, a reflective polarizer,light extraction structures, and a collimator configured at the secondface. At the second face the mirror may e.g. be a wavelength selectivemirror or a mirror including a hole. In the latter embodiment, light maybe reflected back into the body but part of the light may escape via thehole. Especially, in embodiments the optical element may be configuredat a distance of about 0.01-1 mm, such as 0.1-1 mm from the body. Thismay especially apply for e.g. mirrors, wherein optical coupling is notdesired.

When optical coupling is desired, such as with an optical element, likea CPC or a mixing element, downstream of the (part of the) body wherethe luminescent material is located, an optically transparent interfacematerial may be applied. In yet other embodiments, when no opticallytransparent interface material is applied, the average distance betweentwo elements being in optical contact may especially be about at maximumthe wavelength of relevance, such as the wavelength of an emissionmaximum. Hence, when optical contact is desired, there may be physicalcontact. Even in such embodiments, there may be a non-zero averagedistance, but then equal to or lower than the wavelength of interest.

In specific embodiments, especially when no optical contact is desired,the average distance may be as indicated above but at a few places, forinstance for configuration purposes, there may be physical contact. Forinstance, there may be contact with the edge faces over less than 10%,such as over less than 5% of the total area of the side faces. Hence,the minimum average distance may be as defined e.g. above and if thereis physical contact, this physical contact may be with at maximum 10% ofthe surface area of the surface with which the element (mirror and/orheat sink) is in physical contact, such as at maximum 5%, like atmaximum 2%, even more especially at maximum 1%. For instance, for theside faces an average distance may e.g. be between ca 2 and 10 μm (thelower limit basically determined as being a few times the wavelength ofinterest; here, assuming e.g. visible light). This may be achieved byhaving physical contact (to secure that distance) over less than 1% ofthe total area of that respective side face.

For instance, a heat sink or a reflector, or the relevant surface mayhave some protrusions, like a surface roughness, by which there may becontact between the surface and the element, but in average the distanceis at least λ_(i) (or more, see also above) (in order to essentiallyprevent optical contact), but there is physical contact with equal to orless than 10% of the surface of the body (to which the element may bethermally coupled and/or optically not coupled), especiallysubstantially less.

In embodiments, optical elements may be included at one or more of theside faces. In particular, anti-reflection coatings may be applied toenhance coupling efficiency of the (excitation) light source lightand/or (wavelength selective) reflection coatings for the convertedlight.

Downstream of the radiation exit window, optionally an optical filtermay be arranged. Such optical filter may be used to remove undesiredradiation. For instance, when the lighting device should provide redlight, all light other than red may be removed. Hence, in a furtherembodiment the lighting device further comprises an optical filterconfigured downstream of the radiation exit window and configured toreduce the relative contribution of undesired light in the converterradiation (downstream of the radiation exit window). For filtering outlight source light, optionally an interference filter may be applied.

In yet a further embodiment, the lighting device further comprises acollimator configured downstream of the radiation exit window (of thehighest order luminescent concentrator) and configured to collimate theconverter radiation. Such collimator, like e.g. a CPC (compoundparabolic concentrator), may be used to collimate the light escapingfrom the radiation exit window and to provide a collimated orpre-collimated beam of light. Herein, the terms “collimated”,“precollimated” and similar terms may especially refer to a light beamhaving a solid angle (substantially) smaller than 2π.

As indicated above, the lighting device may comprise a plurality oflight sources. This plurality of light sources may be configured toprovide light source light to a single side or face or to a plurality offaces; see further also below. When providing light to a plurality offaces, in general each face will receive light of a plurality of lightsources (a subset of the plurality of light sources). Hence, inembodiments a plurality of light sources will be configured to providelight source light to a radiation input face. Also, this plurality oflight sources will in general be configured in a row or a plurality ofrows. Hence, the light transmissive body is elongated, the plurality oflight sources may be configured in a row, which may be substantiallyparallel to the axis of elongated of the light transmissive body. Therow of light sources may have substantially the same length as theelongated light transmissive body. Hence, in the light transmissive bodyhas a length (L) in the range of about 80-120% of the second length (L2)of the row of light sources; or the row of light sources has a length inthe range of about 80-120% of the length of the light transmissive body.

The light sources may be configured to provide light with a wavelengthselected from the range of UV (including near UV), visible, and infrared(including near IR). Especially, the light sources are light sourcesthat during operation emit (light source light) at least light at awavelength selected from the range of 200-490 nm, especially lightsources that during operation emit at least light at wavelength selectedfrom the range of 360-490 nm, such as 400-490 nm, even more especiallyin the range of 430-490 nm, such as 440-490 nm, such as at maximum 480nm. This light may partially be used by the luminescent material. Hence,in a specific embodiment, the light source is configured to generateblue light. In a specific embodiment, the light source comprises a solidstate light source (such as a LED or laser diode). The term “lightsource” may also relate to a plurality of light sources, such as e.g.2-2000, such as 2-500, like 2-100, e.g. at least 4 light sources, suchas in embodiments especially 4-80 (solid state) light sources, thoughmany more light sources may be applied. Hence, in embodiments 4-500light sources may be applied, like e.g. 8-200 light sources, such as atleast 10 light sources, or even at least 50 light sources. The term“light source” may also relate to one or more light sources that aretailored to be applied for such light concentrating luminescentconcentrators, e.g. one or more LED's having a long elongated radiatingsurface matching the long elongated light input surfaces of theelongated luminescent concentrator. Hence, the term LED may also referto a plurality of LEDs. Hence, as indicated herein, the term “solidstate light source” may also refer to a plurality of solid state lightsources. In an embodiment (see also below), these are substantiallyidentical solid state light sources, i.e. providing substantiallyidentical spectral distributions of the solid state light sourceradiation. In embodiments, the solid state light sources may beconfigured to irradiate different faces of the light transmissive body.Further, the term “light source” may in embodiments also refer to aso-called chips-on-board (COB) light source. The term “COB” especiallyrefers to LED chips in the form of a semiconductor chip that is neitherencased nor connected but directly mounted onto a substrate, such as aPCB (“printed circuit board”) or comparable. Hence, a plurality ofsemiconductor light sources may be configured on the same substrate. Inembodiments, a COB is a multi LED chip configured together as a singlelighting module.

The lighting device comprises a plurality of light sources. Especially,the light source light of the plurality (m) of light sources havespectral overlap, even more especially, they are of the same type andprovide substantial identical light (having thus substantial the samespectral distribution). Hence, the light sources may substantially havethe same emission maximum (“peak maximum”), such as within a bandwidthof 10 nm, especially within 8 nm, such as within 5 nm (e.g. obtained bybinning) However, in yet other embodiments, the lighting device maycomprise a single light source, especially a solid state light sourcehaving a relatively large die. Hence, herein also the phrase “one ormore light sources” may be applied.

In embodiments, there may be two or more different luminescentmaterials, such as e.g. when applying two or more different lighttransmissive bodies. In such embodiments, the light sources may compriselight sources with two or more different emission spectra enablingexcitation of two different luminescent materials. Such two or moredifferent light sources may belong to different bins.

The light sources are especially configured to provide a blue opticalpower (W_(opt)) of at least 0.2 Watt/mm² to the light transmissive body,i.e. to the radiation input face(s). The blue optical power is definedas the energy that is within the energy range that is defined as bluepart of the spectrum (see also below). Especially, the photon flux is inaverage at least 4.5*10¹⁷ photons/(s·mm²), such as at least 6.0*10¹⁷photons/(s·mm²). Assuming blue (excitation) light, this may e.g.correspond to a blue power (W_(opt)) provided to at least one of theradiation input faces of in average at least 0.067 Watt/mm² and 0.2Watt/mm², respectively. Here, the term “in average” especially indicatesan average over the area (of the at least one of the radiation inputsurfaces). When more than one radiation input surface is irradiated,then especially each of these radiation input surfaces receives suchphoton flux. Further, especially the indicated photon flux (or bluepower when blue light source light is applied) is also an average overtime.

In yet a further embodiment, especially for (DLP (digital lightprocessing)) projector applications, the plurality of light sources areoperated in pulsed operation with a duty cycle selected from the rangeof 10-80%, such as 25-70%.

In yet a further embodiment, especially for (LCD or DLP) projectorapplications using dynamic contrast technologies, such as e.g. describedin WO0119092 or USRE42428 (E1), the plurality of light sources areoperated in video signal content controlled PWM pulsed operation with aduty cycle selected from the range of 0.01-80%, such as 0.1-70%.

In yet a further embodiment, especially for (LCD or DLP) projectorapplications using dynamic contrast technologies, such as e.g. describedin US patent WO0119092 or U.S. Pat. No. 6,631,995 (B2), the plurality oflight sources are operated in video signal content controlled intensitymodulated operation with intensity variations selected from the range of0.1-100%, such as 2-100%.

The lighting device may comprise a plurality of luminescentconcentrators, such as in the range of 2-50, like 2-20 lightconcentrators (which may e.g. be stacked).

The light concentrator may radiationally be coupled with one or morelight sources, especially a plurality of light sources, such as 2-1000,like 2-50 light sources. The term “radiationally coupled” especiallymeans that the light source and the light concentrator are associatedwith each other so that at least part of the radiation emitted by thelight source is received by the light concentrator (and at least partlyconverted into luminescence). Instead of the term “luminescence” alsothe terms “emission” or “emission radiation” may be applied.

Hence, the luminescent concentrator receives at one or more radiationinput faces radiation (pump radiation) from an upstream configured lightconcentrator or from upstream configured light sources. Further, thelight concentrator comprises a luminescent material configured toconvert at least part of a pump radiation received at one or moreradiation input faces into luminescent material radiation, and theluminescent concentrator configured to couple at least part of theluminescent material radiation out at the radiation exit window asconverter radiation. This converter radiation is especially used ascomponent of the lighting device light.

The phrase “configured to provide luminescent material radiation at theradiation exit window” and similar phrases especially refers toembodiments wherein the luminescent material radiation is generatedwithin the luminescent concentrator (i.e. within the light transmissivebody), and part of the luminescent material radiation will reach theradiation exit window and escape from the luminescent concentrator.Hence, downstream of the radiation exit window the luminescent materialradiation is provided. The converter radiation, downstream of theradiation exit window comprises at least the luminescent materialradiation escaped via the radiation exit window from the lightconverter. Instead of the term “converter radiation” also the term“light concentrator light” may be used. Pump radiation can be applied toa single radiation input face or a plurality of radiation input faces.

In embodiments, the length (L) is selected from the range of 1-100 cm,such as especially 2-50 cm, like at least 3 cm, such as 5-50 cm, like atmaximum 30 cm. This may thus apply to all luminescent concentrators.However, the range indicates that the different luminescentconcentrators may have different lengths within this range.

In yet further embodiments, the elongated light transmissive body (ofthe luminescent concentrator) comprises an elongated ceramic body. Forinstance, luminescent ceramic garnets doped with Ce³⁺ (trivalent cerium)can be used to convert blue light into light with a longer wavelength,e.g. within the green to red wavelength region, such as in the range ofabout 500-750 nm, or even in the cyan. To obtain sufficient absorptionand light output in desired directions, it is advantageous to usetransparent rods (especially substantially shaped as beams). Such rodcan be used as light concentrator, converting light source light intoconverter radiation and providing at an exit surface (a substantialamount of) (concentrated) converter radiation. Lighting devices based onlight concentrators may e.g. be of interest for projector applications.For projectors, red, yellow, green and blue luminescent concentratorsare of interest. Green and/or yellow luminescent rods, based on garnets,can be relatively efficient. Such concentrators are especially based onYAG:Ce (i.e. Y₃Al₅O₁₂:Ce³⁺) or LuAG, which can be indicated as(Y_(1-x)Lu_(x))₃Al₅O₁₂:Ce³⁺, where 0≤x≤1, such as in embodimentsLu₃Al₅O₁₂:Ce³⁺. ‘Red’ garnets can be made by doping a YAG-garnet with Gd(“YGdAG”). Cyan emitters can be made by e.g. replacing (part of the) Al(in e.g. LuAG) by Ga (to provide “LuGaAG”). Blue luminescentconcentrators can be based on YSO (Y₂SiO₅:Ce³⁺) or similar compounds orBAM (BaMgAl₁₀O₁₇:Eu²⁺) or similar compounds, especially configured assingle crystal(s). The term similar compounds especially refer tocompounds having the same crystallographic structure but where one ormore cations are at least partially replaced with another cation (e.g. Yreplacing with Lu and/or Gd, or Ba replacing with Sr). Optionally, alsoanions may be at least partially replaced, or cation-anion combinations,such as replacing at least part of the Al—O with Si—N.

Hence, especially the elongated light transmissive body comprises aceramic material configured to wavelength convert at least part of the(blue) light source light into converter radiation in e.g. one or moreof the green, yellow and red, which converter radiation at least partlyescapes from the radiation exit window.

In embodiments, the ceramic material especially comprises anA₃B₅O₁₂:Ce³⁺ ceramic material (“ceramic garnet”), wherein A comprisesyttrium (Y) and/or lutetium (Lu) and/or gadolinium (Gd), and wherein Bcomprises aluminum (Al) and/or gallium (Ga), especially at least Al. Asfurther indicated below, A may also refer to other rare earth elementsand B may include Al only, but may optionally also include gallium. Theformula A₃B₅O₁₂:Ce³⁺ especially indicates the chemical formula, i.e. thestoichiometry of the different type of elements A, B and O (3:5:12).However, as known in the art the compounds indicated by such formula mayoptionally also include a small deviation from stoichiometry.

In yet a further aspect, the invention also provides such elongatedlight transmissive body per se, i.e. an elongated light transmissivebody having a first face and a second face, these faces especiallydefining the length (L) of the elongated light transmissive body, theelongated light transmissive body comprising one or more radiation inputfaces and a radiation exit window, wherein the second face comprises theradiation exit window, wherein the elongated light transmissive bodycomprises a ceramic material configured to wavelength convert at leastpart of (blue) light source light into converter radiation, such as (atleast) one or more of green, yellow, and red converter radiation (whichat least partly escapes from the radiation exit window when theelongated light transmissive body is irradiated with blue light sourcelight), wherein the ceramic material comprises an A₃B₅O₁₂:Ce³⁺ ceramicmaterial as defined herein. Such light transmissive body can thus beused as light converter. Especially, such light transmissive body hasthe shape of a cuboid.

As indicated above, in embodiments the ceramic material comprises agarnet material. However, also other (crystallographic) cubic systemsmay be applied. Hence, the elongated body especially comprises aluminescent ceramic. The garnet material, especially the ceramic garnetmaterial, is herein also indicated as “luminescent material”. Theluminescent material comprises an A₃B₅O₁₂:Ce³⁺ (garnet material),wherein A is especially selected from the group consisting of Sc, Y, Tb,Gd, and Lu (especially at least Y and/or Lu, and optionally Gd), whereinB is especially selected from the group consisting of Al and Ga(especially at least Al). More especially, A (essentially) comprises (i)lutetium (Lu), (ii) yttrium, (iii) yttrium (Y) and lutetium (Lu), (iv)gadolinium (Gd), optionally in combination with one of theaforementioned, and B comprises aluminum (Al) or gallium (Ga) or acombination of both. Such garnet is be doped with cerium (Ce), andoptionally with other luminescent species such as praseodymium (Pr).

As indicated above, the element A may especially be selected from thegroup consisting of yttrium (Y) and gadolinium (Gd). Hence, A₃B₅O₁₂:Ce³⁺especially refers to (Y_(1-x)Gd_(x))₃B₅O₁₂:Ce³⁺, wherein especially x isin the range of 0.1-0.5, even more especially in the range of 0.2-0.4,yet even more especially 0.2-0.35. Hence, A may comprise in the range of50-90 atom % Y, even more especially at least 60-80 atom % Y, yet evenmore especially 65-80 atom % of A comprises Y. Further, A comprises thusespecially at least 10 atom % Gd, such as in the range of 10-50 atom %Gd, like 20-40 atom %, yet even more especially 20-35 atom % Gd.

Especially, B comprises aluminum (Al), however, B may also partlycomprise gallium (Ga) and/or scandium (Sc) and/or indium (In),especially up to about 20% of Al, more especially up to about 10% of Almay be replaced (i.e. the A ions essentially consist of 90 or more mole% of Al and 10 or less mole % of one or more of Ga, Sc and In); B mayespecially comprise up to about 10% gallium. Therefore, B may compriseat least 90 atom % Al. Hence, A₃B₅O₁₂:Ce³⁺ especially refers to(Y_(1-x)Gd_(x))₃Al₅O₁₂:Ce³⁺, wherein especially x is in the range of0.1-0.5, even more especially in the range of 0.2-0.4.

In another variant, B (especially Al) and O may at least partly bereplaced by Si and N. Optionally, up to about 20% of Al—O may bereplaced by Si—N, such as up to 10%.

For the concentration of cerium, the indication n mole % Ce indicatesthat n % of A is replaced by cerium. Hence, A₃B₅O₁₂:Ce³⁺ may also bedefined as (A_(1-n)Ce_(n))₃B₅O₁₂, with n being in the range of0.001-0.035, such as 0.0015-0.01. Therefore, a garnet essentiallycomprising Y and mole Ce may in fact refer to((Y_(1-x)Gd_(x))_(1-n)Ce_(n))₃B₅O₁₂, with x and n as defined above.

Especially, the ceramic material is obtainable by a sintering processand/or a hot pressing process, optionally followed by an annealing in an(slightly) oxidizing atmosphere. The term “ceramic” especially relatesto an inorganic material that is—amongst others—obtainable by heating a(poly crystalline) powder at a temperature of at least 500° C.,especially at least 800° C., such as at least 1000° C., like at least1400° C., under reduced pressure, atmospheric pressure or high pressure,such as in the range of 10⁻⁸ to 500 MPa, such as especially at least 0.5MPa, like especially at least 1 MPa, like 1 to about 500 MPa, such as atleast 5 MPa, or at least 10 MPa, especially under uniaxial or isostaticpressure, especially under isostatic pressure. A specific method toobtain a ceramic is hot isostatic pressing (HIP), whereas the HIPprocess may be a post-sinter HIP, capsule HIP or combined sinter-HIPprocess, like under the temperature and pressure conditions as indicateabove. The ceramic obtainable by such method may be used as such, or maybe further processed (like polishing). A ceramic especially has densitythat is at least 90% (or higher, see below), such as at least 95%, likein the range of 97-100%, of the theoretical density (i.e. the density ofa single crystal). A ceramic may still be polycrystalline, but with areduced, or strongly reduced volume between grains (pressed particles orpressed agglomerate particles). The heating under elevated pressure,such as HIP, may e.g. be performed in an inert gas, such as comprisingone or more of N₂ and argon (Ar). Especially, the heating under elevatedpressures is preceded by a sintering process at a temperature selectedfrom the range of 1400-1900° C., such as 1500-1800° C. Such sinteringmay be performed under reduced pressure, such as at a pressure of 10⁻²Pa or lower. Such sintering may already lead to a density of in theorder of at least 95%, even more especially at least 99%, of thetheoretical density. After both the pre-sintering and the heating,especially under elevated pressure, such as HIP, the density of thelight transmissive body can be close to the density of a single crystal.However, a difference is that grain boundaries are available in thelight transmissive body, as the light transmissive body ispolycrystalline. Such grain boundaries can e.g. be detected by opticalmicroscopy or SEM. Hence, herein the light transmissive body especiallyrefers to a sintered polycrystalline having a density substantiallyidentical to a single crystal (of the same material). Such body may thusbe highly transparent for visible light (except for the absorption bythe light absorbing species such as especially Ce³⁺).

The luminescent concentrator may also be a crystal, such as a singlecrystal. Such crystals can be grown/drawn from the melt in a highertemperature process. The large crystal, typically referred to as boule,can be cut into pieces to form the light transmissive bodies. Thepolycrystalline garnets mentioned above are examples of materials thatcan alternatively also be grown in single crystalline form.

After obtaining the light transmissive body, the body may be polished.Before or after polishing an annealing process (in an oxidativeatmosphere) may be executed, especially before polishing. In a furtherspecific embodiment, the annealing process lasts for at least 2 hours,such as at least 2 hours at least 1200° C. Further, especially theoxidizing atmosphere comprises for example O₂.

Instead of cerium doped garnets, or in addition to such garnets, alsoother luminescent materials may be applied, e.g. embedded in organic orinorganic light transmissive matrixes, as luminescent concentrator. Forinstance, quantum dots and/or organic dyes may be applied and may beembedded in transmissive matrices like e.g. polymers, like PMMA, orpolysiloxanes, etc. etc. Other light transmissive material as hostmatrix may be used as well, see also below.

Quantum dots are small crystals of semiconducting material generallyhaving a width or diameter of only a few nanometers. When excited byincident light, a quantum dot emits light of a color determined by thesize and material of the crystal. Light of a particular color cantherefore be produced by adapting the size of the dots. Most knownquantum dots with emission in the visible range are based on cadmiumselenide (CdSe) with a shell such as cadmium sulfide (CdS) and zincsulfide (ZnS). Cadmium free quantum dots such as indium phosphode (InP),and copper indium sulfide (CuInS₂) and/or silver indium sulfide (AgInS₂)can also be used. Quantum dots show very narrow emission band and thusthey show saturated colors. Furthermore, the emission color can easilybe tuned by adapting the size of the quantum dots. Any type of quantumdot known in the art may be used in the present invention. However, itmay be preferred for reasons of environmental safety and concern to usecadmium-free quantum dots or at least quantum dots having a very lowcadmium content.

Instead of quantum dots or in addition to quantum dots, also otherquantum confinement structures may be used. The term “quantumconfinement structures” should, in the context of the presentapplication, be understood as e.g. quantum wells, quantum dots, quantumrods, or nano-wires.

Organic phosphors can be used as well. Examples of suitable organicphosphor materials are organic luminescent materials based on perylenederivatives, for example compounds sold under the name Lumogen® by BASF.Examples of suitable compounds include, but are not limited to, Lumogen®Red F305, Lumogen® Orange F240, Lumogen® Yellow F083, and Lumogen® F170.

Several color conversion schemes may be possible. Especially, however,the Stokes shift is relatively small. Especially, the Stokes shift,defined as the difference (in wavelength) between positions of the bandmaxima of the light source used for pumping and the light which isemitted, is not larger than 100 nm; especially however, the Stokes shiftis at least about 10 nm, such as at least about 20 nm. This mayespecially apply to the light source light to first luminescent materialradiation conversion, but also apply to the second pump radiation tosecond luminescent material radiation conversion, etc.

In embodiments, the plurality of light sources are configured to provideUV radiation as first pump radiation, and the luminescent concentratorsare configured to provide one or more of blue and green first converterradiation. In yet other embodiments, the plurality of light sources areconfigured to provide blue radiation as first pump radiation, and theluminescent concentrators are configured to provide one or more of greenand yellow first converter radiation. Note, as also indicated below,such embodiments may also be combined.

The lighting device may further comprise a cooling element in thermalcontact with the luminescent concentrator. The cooling element can be aheatsink or an actively cooled element, such as a Peltier element.Further, the cooling element can be in thermal contact with the lighttransmissive body via other means, including heat transfer via air orwith an intermediate element that can transfer heat, such as a thermalgrease. Especially, however, the cooling element is in physical contactwith the light transmissive body. The term “cooling element” may alsorefer to a plurality of (different) cooling elements.

Hence, the lighting device may include a heatsink configured tofacilitate cooling of the solid state light source and/or luminescentconcentrator. The heatsink may comprise or consist of copper, aluminum,silver, gold, silicon carbide, aluminum nitride, boron nitride, aluminumsilicon carbide, beryllium oxide, silicon-silicon carbide, aluminumsilicon carbide, copper tungsten alloys, copper molybdenum carbides,carbon, diamond, graphite, and combinations of two or more thereof.Alternatively or additionally, the heatsink may comprise or consist ofaluminum oxide. The term “heatsink” may also refer to a plurality of(different) heatsink. The lighting device may further include one ormore cooling elements configured to cool the light transmissive body.With the present invention, cooling elements or heatsinks may be used tocool the light transmissive body and the same or different coolingelements or heatsinks may be used to cool the light sources. The coolingelements or heatsinks may also provide interfaces to further coolingmeans or allow cooling transport to dissipate the heat to the ambient.For instance, the cooling elements or heatsinks may be connected to heatpipes or a water cooling systems that are connect to more remotelyplaced heatsinks or may be directly cooled by air flows such asgenerated by fans. Both passive and active cooling may be applied.

In specific embodiments, there is no physical contact between the heatsink (or cooling elements) and the light transmissive body. Especially,the average is at least the intensity averaged wavelength of light thatis transmitted by luminescence of luminescent material. In embodiments,the average between the light transmissive body and the heatsink orcooling element is at least 1 μm, such as at least 2 μm, like at least 5μm. Further, for a good heat transfer the average distance between thelight transmissive body and the heatsink or cooling elements is notlarger than 50 μm, such as not larger than 25 μm, like not larger than20 μm, such as equal to or smaller than 15 μm, like at maximum 10 μm.

Therefore, in embodiments the lighting device may further comprise aheat sink having an average distance to the elongated light transmissivebody of at least 1 μm, such as at least 2 μm, like especially at least 5μm, or wherein the heat dissipating element is in physical contact withat maximum 10%, such as at maximum 5% of a total area of the sideface(s) of the elongated light transmissive body. The average is thusespecially not larger than 50 μm. Instead of the term “heat sink” alsothe term cooling element may be applied.

In particular embodiments, the elongated luminescent concentrator isclamped between 2 metal plates or clamped within a housing consisting ofa highly thermal conductive material such way that a sufficient air gapbetween the elongated luminescent concentrator remains present toprovide TIR (total internal reflection) of the light trapped within theelongated luminescent concentrator while a sufficient amount of heat maytraverse from the elongated luminescent concentrator through the air gaptowards the highly thermal conductive housing. The thickness of the airgap is higher than the wavelength of the light, e.g. higher than 0.1 μm,e.g. higher 0.5 μm. The elongated luminescent concentrator is secured inthe housing by providing small particles between the elongatedluminescent concentrator and the housing, such as small spheres or rodshaving a diameter higher than 0.1 μm, e.g. higher 0.5 μm, like at least1 μm, such as at least 5 μm, especially equal to or smaller than 20 μm,such as equal to or smaller than 10 μm (see also above defined average).

Alternatively, the elongated luminescent concentrator may be secured inthe housing by providing some surface roughness on the surfaces of thehighly thermal conductive housing touching the elongated luminescentconcentrator, the surface roughness varying over a depth higher than 0.1μm, e.g. higher 0.5 μm, preferably equal to or smaller than about 10 μm.

The density of such spheres, rods or touch points of a rough surface ofthe highly thermal conductive housing is relatively very small, suchthat most of the surface area of the elongated light transmissive bodyremains untouched securing a high level of TIR reflections within of thelight trapped within the elongated light transmissive body.

The lighting device may thus essentially consist of the elongated lighttransmissive body comprising a luminescent material and one or more,especially a plurality of light sources, which pump the luminescentmaterial to provide luminescent material light, that escapes from aradiation exit window (of an end face (second face)).

Further, the lighting device may comprise an optical element, such as aCPC or (other) extraction optical element, which may be configureddownstream of the light transmissive body, but which in embodiments maybe integrated with the light transmissive body.

Optionally, between this optical element and the light transmissivebody, a radiation mixing element may be configured. Hence, a section ofthe light transmissive body of an additional element may be configuredthat acts as an optical mixing rod (preferably not round, but e.g.hexagonal) between the converters and the CPC (or extraction opticalelement). Alternatively or additionally, the extraction optical elementis designed such that it also mixes the light.

Further, the lighting device may comprise one or more holding elementsfor holding the light transmissive body. Especially, these holdingelements have contact with the edge faces, but only with a small partthereof to minimize losses of light. For instance, the holdingelement(s), like clamping device (s) have contact with the edge facesover less than 10%, such as over less than 5% of the total area of theside faces. Further, the lighting device may comprise a heat sink and/ora cooling element. The holding element(s) may be comprised by the heatsink and/or cooling element.

The lighting device may be part of or may be applied in e.g. officelighting systems, household application systems, shop lighting systems,home lighting systems, accent lighting systems, spot lighting systems,theater lighting systems, architectural lighting, fiber-opticsapplication systems, projection systems, self-lit display systems,pixelated display systems, segmented display systems, warning signsystems, medical lighting application systems, indicator sign systems,decorative lighting systems, portable systems, automotive applications,green house lighting systems, horticulture lighting, or LCDbacklighting, etc. The lighting device may also be part of or may beapplied in e.g. material curing systems, additive manufacturing systems,metrology systems, UV sterilization system, (IR) imaging systems, fiberillumination systems, etc. In an aspect, the invention also provides aprojection system or a luminaire comprising the lighting device asdescribed herein, or a plurality of such lighting devices.

In yet a further aspect, the invention provides a projector comprisingthe lighting device as defined herein. As indicated above, of course thelight projector may also include a plurality of such lighting devices.

In yet a further aspect, the invention also provides a lighting systemconfigured to provide lighting system light, the lighting systemcomprising one or more lighting devices as defined herein. Here, theterm “lighting system” may also be used for a (digital) projector.Further, the lighting device may be used for e.g. stage lighting (seefurther also below), or architectural lighting. Therefore, inembodiments the invention also provides a lighting system as definedherein, wherein the lighting system comprises a digital projector, astage lighting system or an architectural lighting system. The lightingsystem may comprise one or more lighting devices as defined herein andoptionally one or more second lighting devices configured to providesecond lighting device light, wherein the lighting system lightcomprises (a) one or more of (i) the converter radiation as definedherein, and optionally (b) second lighting device light. Hence, theinvention also provides a lighting system configured to provide visiblelight, wherein the lighting system comprises at least one lightingdevice as defined herein. For instance, such lighting system may alsocomprise one or more (additional) optical elements, like one or more ofoptical filters, collimators, reflectors, wavelength converters, lenselements, etc. The lighting system may be, for example, a lightingsystem for use in an automotive application, like a headlight. Hence,the invention also provides an automotive lighting system configured toprovide visible light, wherein the automotive lighting system comprisesat least one lighting device as defined herein and/or a digitalprojector system comprising at least one lighting device as definedherein. Especially, the lighting device may be configured (in suchapplications) to provide red light. The automotive lighting system ordigital projector system may also comprise a plurality of the lightingdevices as described herein.

Alternatively, the lighting device may be designed to provide highintensity UV radiation, e.g. for 3D printing technologies or UVsterilization applications. Alternatively, the lighting device may bedesigned to provide a high intensity IR light beam, e.g., to project IRimages for (military) training purposes.

The term white light herein, is known to the person skilled in the art.It especially relates to light having a correlated color temperature(CCT) between about 2000 and 20000 K, especially 2700-20000 K, forgeneral lighting especially in the range of about 2700 K and 6500 K, andfor backlighting purposes especially in the range of about 7000 K and20000 K, and especially within about 15 SDCM (standard deviation ofcolor matching) from the BBL (black body locus), especially within about10 SDCM from the BBL, even more especially within about 5 SDCM from theBBL, such as within about 3 SDCM from the BBL.

The terms “violet light” or “violet emission” especially relates tolight having a wavelength in the range of about 380-440 nm. The terms“blue light” or “blue emission” especially relates to light having awavelength in the range of about 440-490 nm (including some violet andcyan hues). The terms “green light” or “green emission” especiallyrelate to light having a wavelength in the range of about 490-560 nm.The terms “yellow light” or “yellow emission” especially relate to lighthaving a wavelength in the range of about 560-570 nm. The terms “orangelight” or “orange emission” especially relate to light having awavelength in the range of about 570-600. The terms “red light” or “redemission” especially relate to light having a wavelength in the range ofabout 600-780 nm. The term “pink light” or “pink emission” refers tolight having a blue and a red component. The terms “visible”, “visiblelight” or “visible emission” refer to light having a wavelength in therange of 380-780 nm. The term UV light may be UV-A (315-400 nm); UV-B(280-315 nm) or UV-C (200-280 nm). The term IR light may be light in therange above 780 nm. The term “white light” may in embodiments refer tolight consisting of particular spectral compositions of wavelengths inthe range between 380-780 nm, perceived nearby Planck's black bodyradiators having temperatures of about 1000 K and above.

The elongated light transmissive body, and optionally also the opticalelement, may comprise light transmissive host material (thus not takinginto account the luminescent material, or more especially in embodimentsa luminescent species such as trivalent cerium), especially lighttransparent material for one or more wavelengths in the visible, such asin the green and red, and in general also in the blue. Suitable hostmaterials may comprise one or more materials selected from the groupconsisting of a transmissive organic material, such as selected from thegroup consisting of PE (polyethylene), PP (polypropylene), PEN(polyethylene napthalate), PC (polycarbonate), polymethylacrylate (PMA),polymethylmethacrylate (PMMA) (Plexiglas or Perspex), cellulose acetatebutyrate (CAB), silicone, polyvinylchloride (PVC), polyethyleneterephthalate (PET), including in an embodiment (PETG) (glycol modifiedpolyethylene terephthalate), PDMS (polydimethylsiloxane), and COC (cycloolefin copolymer). Especially, the light transmissive material maycomprise an aromatic polyester, or a copolymer thereof, such as e.g.polycarbonate (PC), poly (methyl)methacrylate (P(M)MA), polyglycolide orpolyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL),polyethylene adipate (PEA), polyhydroxy alkanoate (PHA), polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV),polyethylene terephthalate (PET), polybutylene terephthalate (PBT),polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN);especially, the light transmissive material may comprise polyethyleneterephthalate (PET). Hence, the light transmissive material isespecially a polymeric light transmissive material.

However, in another embodiment the light transmissive material maycomprise an inorganic material. Especially, the inorganic lighttransmissive material may be selected from the group consisting ofglasses, (fused) quartz, transmissive ceramic materials (such asgarnets), and silicones. Glass ceramic materials may also be applied.Also hybrid materials, comprising both inorganic and organic parts maybe applied. Especially, the light transmissive material comprises one ormore of PMMA, transparent PC, or glass.

When a luminescent material, like an inorganic luminescent material,quantum dots, organic molecules, etc., are embedded in a host matrix,the concentration of the luminescent material may in embodiments beselected from the range of 0.01-5 wt % (weight %), such as 0.01-2 wt %.

Hence, it is a further aspect of the invention to provide a lightingsystem comprising one or more lighting devices according to theinvention and a controller for controlling the one or more lightingdevices. Such lighting systems, for example high brightness lightsources, may be used in e.g. front projectors, rear projectors, studiolighting, stage lighting, entertainment lighting, automotive frontlighting, architectural lighting, augmented illumination (incl.data/content), microscopy, metrology, medical applications, e.g. digitalpathology, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIGS. 1a-1e schematically depict some aspects of the invention; and

FIGS. 2a-2e schematically depict some embodiments;

FIGS. 3a-3g schematically depict some embodiments of facets;

FIGS. 4a-4b schematically depict a core-shell embodiment;

FIGS. 5a-5b schematically depict some tapered embodiments;

FIGS. 6a-6e schematically depict some specifically shaped lighttransmissive bodies; FIG. 6f schematically depict some variants ofcross-sections of possible light transmissive bodies; FIG. 6gschematically depict some possible basic shapes of light transmissivebodies (in cross-sectional view);

FIGS. 7a-7d are directed to some embodiments of optical elements; and

FIGS. 8a-8f schematically depict some aspects of light transmissivebodies, optionally with optical elements and/or a mixing portion.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A light emitting device according to the invention may be used inapplications including but not being limited to a lamp, a light module,a luminaire, a spot light, a flash light, a projector, a (digital)projection device, automotive lighting such as e.g. a headlight or ataillight of a motor vehicle, arena lighting, theater lighting andarchitectural lighting.

Light sources which are part of the embodiments according to theinvention as set forth below, may be adapted for, in operation, emittinglight with a first spectral distribution. This light is subsequentlycoupled into a light guide or waveguide; here the light transmissivebody. The light guide or waveguide may convert the light of the firstspectral distribution to another spectral distribution and guides the(converted) light to an exit surface.

An embodiment of the lighting device as defined herein is schematicallydepicted in FIG. 1a . FIG. 1a schematically depicts a lighting device 1comprising a plurality of solid state light sources 10 and a luminescentconcentrator 5 comprising an elongated light transmissive body 100having a first face 141 and a second face 142 defining a length L of theelongated light transmissive body 100. The elongated light transmissivebody 100 comprising one or more radiation input faces 111, here by wayof example two oppositely arranged faces, indicated with references 143and 144 (which define e.g. the width W), which are herein also indicatedas edge faces or edge sides 147. Further the light transmissive body 100comprises a radiation exit window 112, wherein the second face 142comprises the radiation exit window 112. The entire second face 142 maybe used or configured as radiation exit window. The plurality of solidstate light sources 10 are configured to provide (blue) light sourcelight 11 to the one or more radiation input faces 111. As indicatedabove, they especially are configured to provide to at least one of theradiation input faces 111 a blue power W_(opt) of in average at least0.067 Watt/mm². Reference BA indicates a body axis, which will in cuboidembodiments be substantially parallel to the edge sides 147. Reference140 refers to side faces or edge faces in general.

The elongated light transmissive body 100 may comprise a ceramicmaterial 120 configured to wavelength convert at least part of the(blue) light source light 11 into converter radiation 101, such as atleast one or more of green and red converter radiation 101. As indicatedabove the ceramic material 120 comprises an A₃B₅O₁₂:Ce³⁺ ceramicmaterial, wherein A comprises e.g. one or more of yttrium (Y),gadolinium (Gd) and lutetium (Lu), and wherein B comprises e.g. aluminum(Al). References 20 and 21 indicate an optical filter and a reflector,respectively. The former may reduce e.g. non-green light when greenlight is desired or may reduce non-red light when red light is desired.In addition, the former may be used as well to reflect light back intothe transmissive body or waveguide that is not desired as output lightfrom the elongated light transmissive body that subsequently may getre-absorbed in the ceramic material. For instance, a dichroic filter maybe applied. The latter may be used to reflect light back into the lighttransmissive body or waveguide, thereby improving the efficiency. Notethat more reflectors than the schematically depicted reflector may beused. Note that the light transmissive body may also essentially consistof a single crystal, which may in embodiments also be A₃B₅O₁₂:Ce³⁺.

The light sources may in principle be any type of light source, but isin an embodiment a solid state light source such as a Light EmittingDiode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), aplurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or LaserDiodes or OLEDs, or a combination of any of these. The LED may inprinciple be an LED of any color, or a combination of these, but is inan embodiment a blue light source producing light source light in the UVand/or blue color-range which is defined as a wavelength range ofbetween 380 nm and 490 nm. In another embodiment, the light source is anUV or violet light source, i.e. emitting in a wavelength range of below420 nm. In case of a plurality or an array of LEDs or Laser Diodes orOLEDs, the LEDs or Laser Diodes or OLEDs may in principle be LEDs orLaser Diodes or OLEDs of two or more different colors, such as, but notlimited to, UV, blue, green, yellow or red.

The light sources 10 are configured to provide light source light 11,which is used as pump radiation 7. The luminescent material 120 convertsthe light source light into luminescent material radiation 8 (see alsoFIG. 1e ). Light escaping at the light exit window is indicated asconverter radiation 101, and will include luminescent material radiation8. Note that due to reabsorption part of the luminescent materialradiation 8 within the luminescent concentrator 5 may be reabsorbed.Hence, the spectral distribution may be redshifted relative e.g. a lowdoped system and/or a powder of the same material. The lighting device 1may be used as luminescent concentrator to pump another luminescentconcentrator.

As indicated above, the element may include dichroic optical element.Further, the element may include other elements such as e.g. ananti-reflex (AR) coating on one or more surfaces of the elongated lighttransmissive body and of the optical element (at the second face side).It may be advantageous to have an AR coating for the pump light at theoptical entrance window(s), and/or to have an AR coating for theconverted light at the light emission window(s). In addition, reflectivecoatings for the converted light may be applied to the surface areasother than the light extraction window.

FIGS. 1a-1b schematically depict similar embodiments of the lightingdevice. Further, the lighting device may include further opticalelements, either separate from the waveguide and/or integrated in thewaveguide, like e.g. a light concentrating element, such as a compoundparabolic light concentrating element (CPC). The lighting devices 1 inFIG. 1b further comprise a collimator 24, such as a CPC.

As shown in FIGS. 1a-1b and other Figures, the light guide has at leasttwo ends, and extends in an axial direction between a first base surface(also indicated as first face 141) at one of the ends of the light guideand a second base surface (also indicated as second face 142 or “nose”)at another end of the light guide.

FIG. 1c schematically depicts some embodiments of possible ceramicbodies or crystals as waveguides or luminescent concentrators. The facesare indicated with references 141-146.

The first variant, a plate-like or beam-like light transmissive body hasthe faces 141-146. Light sources, which are not shown, may be arrangedat one or more of the faces 143-146 (general indication of the edgefaces is reference 147). Light sources, not shown, may be configured toprovide radiation to one or more edge faces or side faces selected fromfaces 143-146. Alternatively or additionally, Light sources, not shown,may be configured to provide radiation to the first face 141 (one of theend faces).

The second variant is a tubular rod, with first and second faces 141 and142, and a circumferential face 143. Light sources, not shown, may bearranged at one or more positions around the light transmissive body.Such light transmissive body will have a (substantially) circular orround cross-section. The third variant is substantially a combination ofthe two former variants, with two curved and two flat side faces.

In the context of the present application, a lateral surface of thelight guide should be understood as the outer surface or face of thelight guide along the extension thereof. For example in case the lightguide would be in form of a cylinder, with the first base surface at oneof the ends of the light guide being constituted by the bottom surfaceof the cylinder and the second base surface at the other end of thelight guide being constituted by the top surface of the cylinder, thelateral surface is the side surface of the cylinder. Herein, a lateralsurface is also indicated with the term edge faces or side 140.

The variants shown in FIG. 1c are not limitative. More shapes arepossible; i.e. for instance referred to WO2006/054203, which isincorporated herein by reference. The ceramic bodies or crystals, whichare used as light guides, generally may be rod shaped or bar shapedlight guides comprising a height H, a width W, and a length L extendingin mutually perpendicular directions and are in embodiments transparent,or transparent and luminescent. The light is guided generally in thelength L direction. The height H is in embodiments <10 mm, in otherembodiments <5 mm, in yet other embodiments <2 mm. The width W is inembodiments <10 mm, in other embodiments <5 mm, in yet embodiments <2mm. The length L is in embodiments larger than the width W and theheight H, in other embodiments at least 2 times the width W or 2 timesthe height H, in yet other embodiments at least 3 times the width W or 3times the height H. Hence, the aspect ratio (of length/width) isespecially larger than 1, such as equal to or larger than 2, such as atleast 5, like even more especially in the range of 10-300, such as10-100, like 10-60, like 10-20. Unless indicated otherwise, the term“aspect ratio” refers to the ratio length/width. FIG. 1c schematicallydepicts an embodiment with four long side faces, of which e.g. two orfour may be irradiated with light source light.

The aspect ratio of the height H:width W is typically 1:1 (for e.g.general light source applications) or 1:2, 1:3 or 1:4 (for e.g. speciallight source applications such as headlamps) or 4:3, 16:10, 16:9 or256:135 (for e.g. display applications). The light guides generallycomprise a light input surface and a light exit surface which are notarranged in parallel planes, and in embodiments the light input surfaceis perpendicular to the light exit surface. In order to achieve a highbrightness, concentrated, light output, the area of light exit surfacemay be smaller than the area of the light input surface. The light exitsurface can have any shape, but is in an embodiment shaped as a square,rectangle, round, oval, triangle, pentagon, or hexagon.

Note that in all embodiments schematically depicted herein, theradiation exit window is especially configured perpendicular to theradiation input face(s). Hence, in embodiments the radiation exit windowand radiation input face(s) are configured perpendicular. In yet otherembodiments, the radiation exit window may be configured relative to oneor more radiation input faces with an angle smaller or larger than 90°.

FIG. 1c schematically depict some basic embodiments. Especially however,the herein described specific embodiments are applied, such as whereinthe bodies 100 have circular cross-section, but have a shell-likedistribution of the luminescent material and/or are hollow, and/orwherein the bodies have facets at one or more end faces and/or whereinthe bodies taper over at least part of their length.

Note that, in particular for embodiments using a laser light source toprovide light source light, the radiation exit window might beconfigured opposite to the radiation input face(s), while the mirror 21may consist of a mirror having a hole to allow the laser light to passthe mirror while converted light has a high probability to reflect atmirror 21. Alternatively or additionally, a mirror may comprise adichroic mirror.

FIG. 1d very schematically depicts a projector or projector device 2comprising the lighting device 1 as defined herein. By way of example,here the projector 2 comprises at least two lighting devices 1, whereina first lighting device (1 a) is configured to provide e.g. green light101 and wherein a second lighting device (1 b) is configured to providee.g. red light 101. Light source 10 is e.g. configured to provide bluelight. These light sources may be used to provide the projection (light)3. Note that the additional light source 10, configured to provide lightsource light 11, is not necessarily the same light source as used forpumping the luminescent concentrator(s). Further, here the term “lightsource” may also refer to a plurality of different light sources. Theprojector device 2 is an example of a lighting system 1000, whichlighting system is especially configured to provide lighting systemlight 1001, which will especially include lighting device light 101.Such a lighting system may further comprise a controller for controllingthe light source(s).

High brightness light sources are interesting for various applicationsincluding spots, stage-lighting, headlamps and digital light projection.

For this purpose, it is possible to make use of so-called luminescentconcentrators where shorter wavelength light is converted to longerwavelengths in a highly transparent luminescent material. A rod of sucha transparent luminescent material can be used and then it isilluminated by LEDs to produce longer wavelengths within the rod.Converted light which will stay in the luminescent material such as adoped garnet in the waveguide mode and can then be extracted from one ofthe surfaces leading to a luminance and/or radiance gain (FIG. 1e ).

High-brightness LED-based light source for beamer applications appear tobe of relevance. For instance, the high brightness may be achieved bypumping a luminescent concentrator rod by a discrete set of externalblue LEDs, whereupon the phosphor that is contained in the luminescentrod subsequently converts the blue photons into green or red photons.Due to the high refractive index of the luminescent rod host material(typically˜1.8) the converted green or red photons are almost completelytrapped inside the rod due to total internal reflection. At the exitfacet of the rod the photons are extracted from the rod by means of someextraction optics, e.g. a compound parabolic concentrator (CPC), or amicro-refractive structure (micro-spheres or pyramidal structures). As aresult the high luminescent power that is generated inside the rod canbe extracted at a relatively small exit facet, giving rise to a highsource brightness, enabling (1) smaller optical projection architecturesand (2) lower cost of the various components because these can be madesmaller (in particular the, relatively expensive, projection displaypanel).

When luminescent light is generated in an elongated light transmissivebody, three light fractions can be discerned, namely

-   I. Non-TIR light in the cones that are directly transmitted through    one of the four long sides.-   II. Light in the cones that are aligned with the long axis (z-axis)    of the rod, this light sometimes is called TIR-to-Nose light, as    this light is in TIR in the rod until it hits the CPC, and is    transmitted through the CPC. The rays that go into the CPC have an    angle with the z-axis that is smaller than the critical TIR angle    that holds for the n_rod-n_CPC combination. The light in the cone    that is directed towards the tail reflects at the tail via TIR or    via the mirror, and also leaves the rod at the CPC.-   III. The remaining light fraction is in TIR and—in theory, in a    perfect rod—these rays cannot escape from the rod. This fraction is    sometimes called Locked-in TIR light (after the Locked-in syndrome).

If in the round rod the light is generated in the skin, the lightfraction II (TIR-to-Nose) remains unchanged, but fractions I and IIIchange dramatically. FIG. 2a schematically shows the situation thatlight is generated in the center and FIG. 2b schematically shows thesituation that light is generated close to the wall. In both cases, therefractive index of the body material of the elongated lighttransmissive body was chosen to be 1.84 and of the optical element (CPClike optical element) was chosen to be 1.52. With n_rod=1.84, the lightfraction that is escaping from the rod directly (non-TIR) is only 16% ifit is generated in the skin of the rod (skin thickness=0). If light isgenerated on the skin, the non-TIR cone angles to both sidesperpendicular to the skin are identical for the round rod andrectangular rods, which can be proven by simple goniometry. For thatreason, the non-TIR fraction for skin generated light is exactly half ofthe non-TIR fraction in a rectangular rod. The non-TIR loss has beenmodelled analytically for round and rectangular rods. Assuming the lightto be generated at a distance x from the wall, the non-TIR fractionincreases with the relative distance to the wall, as expressed in theratio x/r, wherein r is the radius, which is the case for round rodsonly. Up to x/r=0.4 there is lower non-TIR losses for round rods ascompared to rectangular rods. For a round rod of 2 mm diameter this isup to a depth of 0.4 mm; see FIG. 2c . The radius is indicated withreference y.

With increasing depth of light generation, the non-TIR fractionincreases up to the 57% non-TIR level of the case with light generatedin the center. But with low skin thickness, there is a substantialincrease of the optical efficiency of the rod as compared to therectangular rod. For rectangular rods, the light fractions areessentially independent of the position of light generation. Hence, inan ideal case with light generation on the surface of the round rod,compared to a rectangular rod the efficiency may increase substantially,such as from 68% (rectangular) to 84% (round) (with n_rod=n_CPC=1.84),or such as from 57% (rectangular) to 72% (round) (with n_rod=1.84,n_CPC=1.52). This can be indicated in the following table:

n_rod = 1.84, n_CPC = 1.52 Light fractions n_rod = 1.84, n_rod = 1.84,redistributed in round rod n_CPC = 1.84 n_CPC = 1.52 Locked-In I non-TIR16% 16% 16% + 12% = 28% II TIR-to-Nose 84% 43% 43% + 29% = 72% IIILocked-in TIR — 41% Redistributed

A small absorption length for blue light is the key to having lightgenerated in the skin only. For that reason, an aspect of the inventionis that the phosphor content is sufficiently high. For single crystalLuAG a phosphor concentration of Ce %=0.16-0.25% may lead to anabsorption length of about 0.3 mm-0.2 mm. In order to get an absorptionlength of 0.1 mm, about 0.5% Ce may thus be needed.

Another way of enabling light generation in the skin is by making atubular rod, see FIG. 2d . In this case the light guiding effect iseffective over the full thickness of the ‘ring’. The phosphor content isallowed to be lower as there cannot be phosphor-emitted light from thecore. In an application one should set a limitation to the minimumphosphor content as e.g. substantial blue light transmission through thefull rod should be avoided. FIG. 2d schematically depicts a non-limitingnumber of embodiments in cross-sectional views (see also FIG. 6f ), witha tubular body 100 having a circular cross-section, a tubular body witha rectangular (square) cross-section, and a tubular body with a roundcross-section, wherein by way of example the cavities, indicated withreference 1150, in the former two variants may be filled with a material121, which especially may have in embodiments a refractive index lowerthan the refractive index of the material of the elongated (tubular)body (but higher than air). The distance between the bodies, indicatedwith reference d4 in variant III, may differ along the body axis BA (seealso FIG. 5b ). In embodiments, especially where the cavity 1150 isfilled with a material having essentially the same index of refractionas the material of the adjacent outer body 100, then there may bephysical contact (i.e. d4=0 μm). The cavity may in embodiments also atleast partly be filled with another body 100; in such embodiment acore-shell configuration may be obtained (see also FIGS. 4a-4b ). Whenthe cavity comprises a solid element, such as a body (see also FIG. 4a), the cross-sectional symmetry of the internal body may be differentfrom the external body, though especially they may be the same. In theformer variant, d4 may vary over the cross-section. Referring to FIG. 2d, but e.g. also 2 e, 5 b, transmission perpendicular to the body 100 oflight leads to a double pass. The total transmission through the bodyunder perpendicular radiation with light having a wavelength ofinterest, such as e.g. the wavelength at maximum emission of theluminescent material, is at maximum 50%.

With the embodiment of FIG. 5b , the advantages of a hollow (withcircular cross-section) variant, or a variant wherein a concentration ofthe luminescent material (or activator) is variable over the distance tothe surface, is combined with the variant of tapering, wherein light isconcentrated in a small area. Thereby, the ring shape distribution ofthe light may essentially be reduced. With the downstream opticalelement, e.g. the beam may be shaped.

In specific embodiments, including the embodiment schematically depictedin FIGS. 3b, 3e, 3g (top) and 5 b, wherein hallow bodies 100 areapplied: when the hollow body does not contain another body or materialin the cavity, at the inside a reflector may be arranged.

Hence, especially the following conditions may be applied:

a solid rod: round, oval or elliptical in cross section externally; withsufficient phosphor content to have an absorption length ≤0.4 rodradius; or

a tubular rod, round, oval or elliptical in cross section, with limitedwall thickness, such that inner radius ≥0.6 outer radius; withsufficient phosphor content to have absorption length≤wall thickness.

Another way of enabling light generation in the skin is by realizationof a body 100 in which the luminescent material (or activator)concentration is localized near the outer surface. In this case, therefractive index is essentially constant throughout the complete body.Such embodiments is schematically depicted in FIG. 2 e.

FIG. 2e schematically depicts a variant wherein the luminescent element5 further comprises a first reflector 21 and/or a second reflector 22.The elongated light transmissive body 100 has a first face 141 and asecond face 142 defining a length L of the elongated light transmissivebody 100; wherein the second face 142 comprises a first radiation exitwindow 112. The first reflector 21 is configured at the first face 141and is configured to reflect radiation back into the elongated lighttransmissive body 100. The second reflector 22 has a cross-sectionsmaller than the radiation exit window 112, wherein the first reflector22 is configured to reflect radiation back into the light transmissivebody 100.

Here, the distances between the optical elements 21 and 22 with thelight transmissive body are indicated with references d1 and d2,respectively. Preferably, they have no physical (or optical) contact toallow TIR for rays with high angle of incidence and only reflect lowangle of incidence rays via the mirror. Distances d1 and d2 may e.g. bein the order of 1-50 μm for visible radiation. As indicated above,values of these distances may be indicated as average values.

In other embodiments, however, there may be physical contact between thebody and the optical element 21 (if available) and/or the opticalelement 22 (if available). For instance, upon pressing the mirror to therod, a bare minimum of real material-material contact area is inevitablefrom contact force and material hardness. In case of optical contact,more rays hit the mirror, but the additional loss is still limited ifthe reflectivity of the mirror is high. Further, the distance between alight emitting surface 13 of the light source 10 and the lighttransmissive element is indicated with reference d3. Hence, thesedistances d1, d2, and d3 may each independently be chosen of a range ofat least 1 μm, such as at least 2 μm.

One or more of the end faces may be facetted or may have othermodulations, or may have one or more oblique sides, see FIGS. 3a-3f .For instance, one or more of the first face 141 and the second face 142comprise a plane 1140 comprising surface modulations 1141 therebycreating different modulation angles β relative to the respective plane1140; these angles may be equal to or smaller than e.g. about 45°, suchas at maximum 40°, like in embodiments at maximum 30°, such as equal toor smaller than about 25° (see e.g. FIG. 3d ). Further, in embodiments βis especially at least 15°, such as at least 20°. Especially, the plane1140 comprises n/cm² facets 1142 as modulations 1141, wherein n isselected from the range of 2-2000, such as 4-500. Further, inembodiments, as schematically depicted, there are at least 2 facets 1142having different modulation angles β, such as at least four. There mayalso be a continuous modulation, see FIG. 3c , wherein a kind ofsinusoidal modulation is available.

The body 100 may have a square cross-section or a rounded cross-section.In the latter variant, the modulations are especially modulationsparallel to the radius radii, and not deviations from the radius radii.Thus, the modulations 1141 may have angles γ relative to perpendicularsr1 to the axis of elongation BA selected from the range of 0-90°, suchas in embodiments up to 35°, like in the range of 15-35°, more like inthe range of 25-35° see also FIGS. 3f and 3g . The outcoupling of theluminescence in variants I-II can be increased with 1-5 percent pointsusing facets, such as four facets. The outcoupling of the luminescencein variant III can be increased with 5-10 percent points using facets,such as four facets. Note that in variant I (and III) there is someradial distortion. FIGS. 3b and 3e , and optionally FIG. 3d ,schematically depict facets provided to an end face of a hollow(tubular) body 100. FIG. 3f , and optionally FIG. 3d , schematicallydepicts facets to an end face of a cylindrical body.

FIG. 3g schematically depict three variants of bodies wherein the firstface 141 and/or the second face 142 (here, a single face is depicted)comprises a plurality of facets 1140, here each having four facets 1140.Variant I shows a hollow body 100 having a round cross-section, variant2 schematically depicts a body 100 having a rectangular cross-section,and variant III schematically depicts a body 100 having a roundcross-section. Best results may be obtained with β in the range of15-45°, such as 20-40°, even more such as 25-35°. In a preferredembodiment, the bodies (variant I, II and III) of FIG. 3a-g furthercomprise a reflective surface (not shown in FIG. 3a-g ) facing the firstface (141). The reflective surface is conformal with the shape of thefirst face (141) and is not in direct contact with the first face (141).The gap between the reflective surface and the first face (141) may befilled with air or with a material that has a relative low refractiveindex compared to the material of the elongated light transmissive body(100).

Hence, when especially referring to bodies 100 having a circularcross-section, A primary function of the modulations, such as facets,would be a β modulation (tangential direction), but for a limited numberof modulations, such as especially facets, there may also be(significant) γ modulation. The embodiments of FIG. 3g all have anefficiency increase of about 5-10% relative to bodies 100 without themodulations (here four facets).

Especially, for one or more modulations, such as for one or more facets,especially for essentially all modulations, such as essentially allfacets, the ratio of β/γ≥0.8, such as especially β/γ≥1.0, like β/γ≥1.2.

An advantage of a hollow elongated body is that no scattering can takeplace in the center of the rod. It appears that light scattering in thecenter of a round rod leads to relatively high light losses and shouldbe avoided. However, with a hollow elongated light transmissive body theinside wall introduces a new source of light scattering which can lowerthe performance of the elongated light transmissive body if thescattering is significant. But it is hard and expensive to polish theinside rod wall to a surface smoothness with only low scattering.

With a transparent filling material the light scattering at the insidewall is reduced, as more rays that hit the inside wall are transmittedthrough the interface. The closer the refractive indices of rod andfilling material are, the smaller the change in light direction upontransmission through the interface. Further, with a given (high index)rod material, the critical TIR angle depends on the refractive index ofthe filling material, the more close n_filler is to n_rod, the largerthe critical TIR angle and the more transmission takes place, whiletransmitted light is scattered less than reflected light. Also, theFresnel reflections depend on the refractive indices of both materials,the more close n_filler is to n_rod, the lower the Fresnel reflectionsare (which are subjected to scattering). Scattering at the inside wallis completely vanished if n_filler=n_rod. But also the light guiding ofthe inside wall in no longer there.

In view of the light guiding effect of the inside wall it may beadvantageous to have a filling material with a refractive index that islower than that of the rod.

Hence, the following features may be of relevance: a hollow elongatedlight transmissive body, a filling material that is essentially fullytransparent, with a very low scatter level, essentially no air bubblesor other inclusions in the filling material, and a refractive index ofthe filling material that is in between the refractive indices of airand the elongated light transmissive body.

Further, a rod-in-rod concept may be applied, see FIGS. 4a -4 b.

For instance, rods having the same length and concentration of phosphorfixed along the rod can be applied. Then, the spectral distribution maynot be tunable when irradiation is via the outer rod. Especially, insuch embodiments where the light sources are configured external of therod assembly, the phosphor concentration of outer rod should be lowenough that part of the light source light, such as blue LED light canhit the inner rod.

In embodiments, for blue light one can use high power LED at beginningof the rod which can be just a light guide. Alternatively oradditionally, a LED with e.g. 405 nm can be used that pass the green andred rod and hit the center rod which absorbs 405 nm and exits ˜470 nmblue.

In embodiments, the concentration of the phosphor varies along the rod.If phosphor concentration varies along the rod; more or less blue lightcan hit the red rod, when irradiation is via the outer rod. Adaptingcurrent depending on location of the blue LED, spectrum can be changed.

For extraction of light from the light transmissive body, a CPC(Compound Parabolic concentrator) can be used. For best extraction, therefractive index of the CPC should match with refractive index of therod. The attachment of this CPC to the HLD rod is quite a challengeregarding matching refractive indices rod, glue, CPC and mechanicalstrength. By making the rod from one piece the last part of the rod canbe made completely tapered, in embodiments with increasing diameter forincreasing distance from the cylindrical luminescent converter componentto extract the light from the end side, or in other embodiments withdecreasing diameter for increasing distance from the cylindricalluminescent converter to extract the light from the tapered sidesurface, by which light can be extracted as also collimated by which noCPC is needed which is a big advantage. Another possibility is partlytapering of the rod and adding a CPC after the tapered part. Anadvantage may be that extracted light has much lower etendue or a higherbrightness may be achieved (than with a tapered light transmissivebody), and still the controlled collimation of light with CPC may beobtained.

Both options worked best with hollow cylindrical or elliptical shapedrods in which light is generated close to the outer wall of the rod andwith additional structures on mirror opposite to the light extraction.

Both figures shows embodiments of a luminescent element 5 comprising anelongated light transmissive body 100, the elongated light transmissivebody 100 comprising a side face 140, wherein the elongated lighttransmissive body 100 comprises a luminescent material 120 configured toconvert at least part of a light source light 11 selected from one ormore of the UV, visible light, and IR received by the elongated lighttransmissive body 100 into luminescent material radiation; wherein theelongated light transmissive body 100 has a length L; the elongatedlight transmissive body 100 is hollow over at least part of the length Lthereby defining a cavity 1150.

In FIG. 4a , the elongated light transmissive body 100 is tubularshaped. Further, the elongated light transmissive body 100 has a tubularshape having a cavity 1150 surrounded by the elongated lighttransmissive body.

Also, by way of example in FIG. 4b , the luminescent element 5 furthercomprising an optical element 24 optically coupled to the elongatedlight transmissive body 100, here a dome. In an alternative embodiment,a conical structure may be applied. Such conical structure may taper inthe direction of a radiation entrance window 211 of the optical element(i.e. in the direction of the second face 142 of the light transmissivebody 100 (bodies 100). In alternative embodiments, such conicalstructure may taper in the direction of a radiation exit window 211 ofthe optical element (i.e. in a direction away of the second face 142 ofthe light transmissive body 100 (bodies 100). Note that only by way ofexample the optical element 24 is drawn in combination with the elementcomprising the core-shell(s) configuration. The optical element mayespecially be used in combination with essentially any of the hereindescribed elements 5.

In FIG. 4b , the light transmissive body 100′ is solid.

FIGS. 4a and 4b especially show embodiments of the luminescent element 5comprising a plurality of elongated light transmissive bodies 100, eachelongated light transmissive body 100 comprising a luminescent material120 configured to convert at least part of a light source light 11selected from one or more of the UV, visible light, and IR received bythe elongated light transmissive body 100 into luminescent materialradiation 8. Further, the elongated light transmissive bodies 100 differin one or more of a length L of the elongated light transmissive bodies100, b type of luminescent material 120, c concentration of luminescentmaterial 120, d concentration distribution over the elongated lighttransmissive body 100, and e host matrix for the luminescent material120. As shown, each elongated light transmissive body 100 has an axis ofelongation BA, which are here coinciding. Further, one or more of theelongated light transmissive bodies 100 comprise cavities 1150. In FIG.4a , the smallest elongated body 100, indicated with reference 100′ ismassive, whereas in FIG. 4b the smallest elongated body 100′ alsoincludes a cavity 1150, indicated with reference 1150′. Thenotations′refer to the inner elongated body 100′ and the notations″refer to the outer elongated body 100″. Note that in principle more thantwo elongated bodies 100 may be applied. As shown, the elongated lighttransmissive bodies 100 are configured in a core-shell configurationwherein a smaller elongated light transmissive body 100 is at leastpartly configured in the cavity 1150 of a larger elongated lighttransmissive body 100 and wherein the axes of elongations BA areconfigured parallel. The side faces 140 of adjacent elongated lighttransmissive bodies 100 have no physical contact or only over at maximum10% of their respective surface areas.

FIGS. 4a-4b also show embodiments of the lighting device 1 comprising:

a light source 10 configured to provide light source light 11;

the luminescent element 5 according to any one of the preceding claims,wherein the elongated light transmissive body 100 comprises a radiationinput face 111 and a first radiation exit window 112; wherein theluminescent material 120 is configured to convert at least part of lightsource light 11 received at the radiation input face 111 intoluminescent material radiation 8, and the luminescent element 5configured to couple at least part of the luminescent material radiation8 out at the first radiation exit window 112 as converter radiation 101.

Each elongated light transmissive body 100 has a first face 141 and asecond face 142 defining a length L of the elongated light transmissivebody 100; wherein the side face 140 comprises the radiation input face111, wherein the second face 142 comprises the radiation exit window112. The different lengths are indicated with L′ and L″, respectively,though here the lengths are essentially identical.

One or more light sources 10 are configured to provide light sourcelight to the side face 140 of an outer elongated light transmissive body100 and/or wherein one or more light sources 10 are configured toprovide light source light 11 to one or more first faces 141, whereinthe one or more first faces 141 are end faces, and/or wherein one ormore light sources 10 are configured in a cavity 1150 of an innerelongated light transmissive body 100 and configured to provide lightsource light 11 to the side face of the inner elongated lighttransmissive body 100. In specific embodiments, in a first mode ofoperation the lighting device 1 is configured to provide white light. Inother specific embodiments, the lighting device comprises a first modeof operation wherein colored light is provided. In yet furtherembodiments, the lighting device 1 may further comprise a controlsystem, configured to control the light sources, where the differentlight transmissive bodies 100 are configured to provide luminescentmaterial light with different spectral distributions. In suchembodiments, the spectral distribution of the lighting device light 101may be tunable.

The optical element 24 comprises in the schematically depictedembodiment a radiation entrance window 211 and a radiation exit window212, and essentially consists of light transmissive material.

Embodiments of tapered rods are shown in FIG. 5a-5b . In FIG. 5b , thecross-sectional area may essentially stay constant. Hence, these figuresschematically depict embodiments wherein the elongated lighttransmissive body (100) tapers along at least part of the length of theaxis of elongation (BA). Or, the elongated light transmissive body (100)tapers along at least part of its length L. FIG. 5b schematicallydepicts an embodiment wherein the tubular elongated light transmissivebody (100) tapers along at least part of the length of the axes ofelongation (BA) while maintaining a cross-sectional area perpendicularto the axes of elongation (BA) constant, see the dashed lines in thetapered section. Normally, if the area is becoming smaller, light couldbe extracted or the light is reversed back to the nose.

Because we can make use of recycling of the light, it appeared possibleto make area of the entrance of the optical component, such as a CPC,even smaller than area of cross section of the hollow rod. Part of thelight may thus be recycled at the second face. This embodiment is notdepicted.

A luminescent concentrating body with a specific cross-sectional shapethat enables improved coupling efficiency, improved light extraction,improved cooling, improved converter mounting, improved module assembly,and/or improved light source robustness by features related to thatspecific cross-sectional shape, is herein—amongst others—proposed.

In embodiments, one or more features may include: embedding of the pumpLEDs within linear cavity in the converter; positioning/alignment of theconverter body in the high brightness module; defining the distance frompump LEDs to the converter; reducing the light extraction cones from 4down to 2 resulting in reduced light losses and therefore an increasemodule performance; mounting of multiple converters next to each otheror within each other, enabling spectral tuning of the light sourceoutput; specific converter cross sectional profiles that enable one ormore distinct advantages are I shapes, O shapes, T shapes, U shapes, andmore complex versions.

In embodiments (I) a highest linear optical flux density for irradiationwith LEDs of a luminescent light concentrator, which is needed to keepthe light source dimensions limited and the cost lowest, can begenerated by applying chip scale package LEDs (CSP-LEDs). However,contrary to the thin film flip chip LEDs that are used in for examplethe first generation HLD product, and which are top-emitters (i.e., onlyemitting from the top surface), all currently available CSP LEDs are5-side emitters, resulting in higher light losses as it is difficult tocouple the light that is emitted sidewards from the chips into theconversion rod. Modeling shows a light loss of ca 10% even with arectangular luminescent converter that has a width that is significantlylarger than the width of a CSP LED. By shaping the luminescentconverters such that they surround the pump LEDs, the couplingefficiency can be significantly improved, as in this way almost alllight can be captured by the conversion rod.

FIG. 6a schematically shows an embodiment of an I-shaped luminescentconversion rod for maximum coupling efficiency of pump light. Left, across sectional view of I-shaped conversion rod clamped between two rodholders, sandwiched between two PCB's each having a linear array of5-side emitting CSP-LEDs is shown. In the middle a 3D perspective viewof the conversion rod is shown, and at the right, a variant of lightsource with ceramic substrates on heat spreaders is shown.

Reference 17 refers to and PCB, such as an MCPCB, which is a metal-corePCB (printed circuit board. Reference 18 refers to rod holder orelongated light transmissive body hold, of which e.g. a top rod holderand a bottom rod holder may be available. However, other configurationsmay also be possible. Reference 1150 indicates a cavity.

In embodiments (II), the distance from pump LEDs to the rod iscontrolled by the depth of the groove in the rod that comprises thestack of dies and solder; currently this is handled by a separatemechanical provision in the rod holders making these components complexand expensive. In this embodiment, the rod is simply placed directlybetween the two opposing PCB's, ideally having substantially the samewidth as the rod holder that is rigidly mounted to at least one of thePCBs. In other embodiments both rod holders have the same thickness andare just mounted and fixated in place, enabled by the easy placement ofthe rod; in this case no movable top rod holder is needed anymore thatin the first generation product still needs to be clamped to the rod.Alternative board configurations including ceramic boards are possibleas well.

FIG. 6b schematically depicts a cross sectional view of light sourcewith I-shaped conversion rod where the gap between the top face of thepump LEDs and the rod is determined by the groove in the rod. Here, therod has substantially the same width as the rod holders, where both rodholders are mounted fixed to the boards/heat spreaders.

In embodiments (III) the light conversion is realized by alongitudinally tiled rod, enabling spectral broadening of the overalloutput by using different compositions of the two U-shaped rods. Anadditional feature is realized by independent addressing of the pumpLEDs on the two boards, which enables dynamic tuning of the overalloutput spectrum.

FIG. 6c schematically depicts a schematic cross-sectional view of twolight source embodiments according to the invention comprising twoU-shaped conversion rods forming together an I-shaped conversion body.The pump LEDs on the two opposite boards may be driven independently,enabling temporal variation of the overall output spectrum.

In embodiments (IV) In addition to the tiling of the conversion body, infurther embodiments of the light source the rod holders arelongitudinally tiled for ease of assembly: in this way the two halves ofthe light source can be assembled independently and subsequently bemounted together, e.g. by clamping the corresponding rod holders of thetwo halves to each other, or by using dedicated spacers between theboards. Light extraction optics may be mounted after having assembledthe rods in their holders and the two halves have been mounted together.By using split rod holders, soldering of rod holders directly to bothPCB's (or to the ceramic substrate if used) is enabled.

FIG. 6d shows a schematic cross-sectional view of a light sourceembodiment according to the invention comprising two U-shaped conversionrods forming together an I-shaped conversion body, and where also therod holders are tiled: the module comprises two halves that areseparately assembled and afterwards bolted or clamped together. Left,the corresponding rod holders of both half-modules are clamped togetherupon assembly of the complete module, and right, the rod holders aresoldered (or glued) to the respective boards. Using distance pieces, thetwo half-assemblies are mounted together at the desired distance fromeach other.

Reference 19 refers to a distance element or distance piece. This may bea piece of metal or ceramic material or polymeric material. Especially,the distance element may be a temperature resistant material. Inembodiments, the distance element 19 may be a glass or a ceramicmaterial. In further embodiments, the distance element 19 may be aliquid crystal polymer.

In embodiments (V) the distance from pump LEDs to the rod is controlledby an alignment feature in the circumference of the rod that coincideswith a feature in the mechanics around the rod. This alignment featurecan either be one or more (longitudinal) grooves in the rod, or it canbe (longitudinal) protrusions from the rod.

FIG. 6e schematically depicts a schematic cross-sectional view of lightsource with conversion rod comprising longitudinal features foralignment of the lateral rod position, and optionally grooves forembedding the pump LEDs. On the left, a rod with LED-embedding groovesand rod-alignment grooves is depicted, and on the right, a rod withalignment protrusions is schematically depicted.

Reference 1160 indicates a protrusion.

In embodiments (VI), a tube-shaped luminescent converter is applied. Thehollow center part of this converter may be substantially filled by asecond luminescent converter rod that may have a different compositionthan that of the tube-shaped converter. FIG. 6f schematically depict anon-limiting number of embodiments. It schematically shows crosssectional view of the core of the light source comprising a hollowconversion tube. Pump LEDs as mounted parallel to the tube and potentialirradiating laser diodes irradiating one of the facets of the centerbody, as well as the cooling blocks for cooling the luminescentconverters have been omitted for simplicity.

In an embodiment a tubular converter is applied with a wall thicknesssignificantly smaller than half the outer diameter of the tube. Thecross-sectional shape may be circular or oval, and/or may have flatsides for maximum coupling of pump light from the LEDs into theconverter. The thinner the wall, the smaller the extinction losses asthe 4 escape cones of converted light that are associated with the 4sides of a square or rectangular rod are reduced to only 2 escape cones(this is the limit for an infinitely thin wall; note however that thethickness in combination with activator concentration should be largeenough to enable substantial conversion for practically achievableactivator concentrations in the converter material).

In a further embodiment, a substantially transparent and highlytranslucent rod is positioned inside the luminescent conversion tube,providing independent light guidance in the longitudinal direction ofboth bodies. The outer rod is pumped by blue LEDs mounted parallel tothe rod, while the inner rod acts as a light guide and homogenizer forblue and/or red laser diode light that is coupled into the rod at oneend, where the tube is provided with a mirror to reflect part of theconverted light (emitted towards this end facet). The center rod may beshaped to optimally fill the center cavity, or preferably has apolygonal cross-sectional shape for improved spatial homogenization.Some, preferably forward, scattering may be present in the center rodand/or on the outer surface of the rod to improve the homogeneity of thelight at the exit facet.

In an alternative embodiment, a luminescent conversion rod is mountedwithin the hollow luminescent conversion tube, the rod and the tubehaving different luminescent emission spectra. For maximum convertedlight guidance performance, the center rod preferably has an absorptionlength much smaller than its diameter, or has a substantial square orrectangular shape to prevent the occurrence of more than 4 escape conesin the cross sectional plane.

FIG. 6g schematically depicts some non-limiting examples of bodies incross-sectional views, with massive bodies 100 and with hollow bodies100 having cavities 1150. Would variants I or III be tapering along thelength of the body 100 (i.e. perpendicular to the plane of drawing, a(truncated) pyramid may be obtained. Would variants II or IV be taperingalong the length of the body axis BA, then a (truncated) hexagonalpyramid may be obtained. Would variants III or VI be tapering along thelength of the body axis BA, then a (truncated) cone may be obtained (seee.g. FIG. 5b ).

FIG. 6g amongst others depicts a body 100 with a hexagonalcross-section. Also octagonal cross-sections may be applied. The numberof side faces (in cross-section) may be defined a n, with n being 4 forsquare or rectangular, and being 6 for hexagonal, and in effect beingunlimited for a round cross-section. In embodiments, n is selected fromthe range of 4-50, such as 6-50, like 6-40. In other embodiments, thebody is round (right part of the drawing).

In embodiments, wherein a cylindrical light converter is applied, anefficient light extracting collimator can be applied that results in ahomogeneous light emitting surface without a center hole and withoutsignificant étendue increase, by applying a circular version of a2-dimensional CPC (or an optimized shape close to that). FIG. 7aschematically shows a cross sectional view and a front view, with aschematic longitudinal cross-sectional view (left) and front view(right) of the core of the light source comprising a hollow conversiontube with a light extracting collimator that fills the center gap of thetube. Pump LEDs as well as cooling provisions, which are mountedparallel to the tube, have been omitted for simplicity.

FIG. 7a schematically depicts an embodiment wherein the optical element24 comprises a first wall 1241 and a second wall 1242 surrounding thefirst wall 1241 thereby defining an optical element 24 having aring-like cross-section, wherein the optical element 24 comprises aradiation entrance window 211 and a radiation exit window 212, whereinthe radiation entrance window 211 is optically coupled with a pluralityof elongated light transmissive bodies 100. Note that the samecross-sectional views may apply to a hollow elongated light transmissivebody 100 (including a cavity) optically coupled to such optical element24. The optical element may be hollow or may be a massive bodycomprising light transparent material.

In case of a combination of multiple light converter bodies, a lightextracting optical component such as a solid CPC, a solid truncatedpyramid or a solid truncated cone, is preferably mounted to the bodiesafter the latter ones have been mounted and fixed in position. In thosecases where they are not completely fixed, i.e., can move somewhat,relative to each other, the light extractor may be mounted rigidly toonly one of the converter bodies, e.g. the outer tube, while the innerrod is preferably brought in optical contact with the light extractingoptics via a flexible gel.

In case of a combination of a light converting tube with anon-converting center rod, the light extracting optical component needsto be mounted only to the luminescent converter body (as transmissionthrough the center rod is high even without optical contact).

FIG. 7b schematically depict a non-limiting number of optical elements.Here, especially concentrators are depicted. FIG. 7b schematicallydepicts a revolved CPC (I), a crossed CPC (II), a compound CPC (III), alens-walled CPC (IV), a crossed V-trough concentrator (V), a polygonalCPC (VI), a square elliptical hyperboloid (SEH)(VII), a V-trough (VIII),a compound parabolic concentrator (IX), a compound ellipticalconcentrator (X), and a compound hyperbolic concentrator. Furtheroptions or hybrids between two or more of these may also be possible.

However, also a dome shaped optical element may be applied, see FIGS. 7c(and 4 b), embodiment I.

Optical elements may e.g. increase in diameter with increasing distancefrom the transmissive body, such as shown in most of the drawings,expect for the half sphere or dome in FIG. 7c , embodiment I. However,also e.g. conical structures or 1-dimensionally tapered elements, whereespecially a characteristic width (or diameter) decreases withincreasing distance from the transmissive body could be relevant. Insuch embodiments, light extraction is to the side(s) of the element (atgrazing angles).

Alternatively, an optical element 24 with decreasing outer dimensionsfor increasing distance from the entrance plane can be applied (II).This may create a collimated extracted beam, in contrast to thenon-collimated beam that is emitted from a dome-shaped optical element(I). Alternatively, a wedge-shaped structure may be applied (notdepicted).

FIG. 7a schematically depicts a revolved optical element, such as arevolved CPC. Alternatively, a number of small optical elements may bechosen or a plurality of fibers may be chosen (not shown), which areoptically coupled to the (hollow) light transmissive body 100. FIG. 7dschematically depicts an embodiment wherein a plurality of opticalelements 24 are applied, downstream of the radiation exit window 112.

In embodiments, in case of a shaped converter body that is differentfrom the desired light emitting surface shape, or a combination ofmultiple light converter bodies, a further light mixing portion of theconverter structure may be used that spatially homogenizes the lightbefore being further extracted (and possibly pre-collimated) by theextraction optics. In other words, a mixing portion is provided betweenthe converter body and the beam shaping and light extracting optics.

With the new multi-component manufacturing approaches, concentratorshapes and compositions as presented in this document, most or all ofthese disadvantages may be overcome or may be significantly reduced,resulting in high brightness light sources with significantly reducedcost and with highly improved performance characteristics.

A monolithic luminescent concentrating body is proposed that has arefractive index that is constant throughout that body, while theoptical absorption and/or the emission spectrum is a function oflocation in that body. In particular, a luminescent converter isproposed that has a high optical absorption for pump light in an outerlayer of the body while the inner part of the body has a lowerabsorption for the pump light, preferably is transparent for the pumplight. This can be realized by 2-k extrusion, by co-injection molding(first mold the core of the body, and use that as an insert for themolding of the outer shell of the body), by subsequent gel casting (sameprinciple), or by subsequent pressing (same principle). Upon sinteringof these bodies, a luminescent converter results with the requestedproperties. In a second application, the light extractor body isco-created with the luminescent converter body in the “green phase” by2-k injection molding, pressing, 2-k pressing, or 2-k gel casting, basedon two materials that have different spectral absorption characteristicswhile having the same refractive index. In all cases, the crystalstructures of the 2 (or more) materials are chosen to be very similar toenable successful sintering, to preserve a cubic lattice throughout thewhole body, and prevent second phase formation. This is realized byusing host materials that are very similar, e.g. substantially the samegarnet composition, but with a different doping level of the Ceactivator, or with little deviations in the lattice. Some (small)differences in the garnet host material may also be tolerated, butpreferably these are substantially equal.

The term “2k” refers to “two components”. It may also refer tomulti-component, as the principle of two components may in general alsobe applied for more than two components.

Pressing, such as especially uni-axial pressing, may be applied as well.Pressing may include dry powder pressing or wet suspension pressing.Further, a mold may be used when pressing.

In embodiments, a monolithic converter comprising an outer layer withhigh absorption of pump light and inner part with low absorption of pumplight is proposed. In embodiments a rod or bar is realized withabsorption of pump light in an outer layer and lower absorption of pumplight in the inner part. The rod or bar has a refractive index that isconstant and a crystal structure that is substantially homogeneousthroughout the converter as well. This is realized by 2-componentextrusion, by injection molding of a shell layer around a (molded orextruded) core, or by casting of a shell layer around a casted (or maybeeven molded/extruded) core, after which the composed body is sintered,see FIG. 8a , which shows a monolithic poly-crystalline ceramic bar orrod with luminescent outer layer, indicated with reference 120(luminescent material), and non-luminescent inner part 107; both partshave the same refractive index and coefficient of thermal expansion, butdifferent spectral absorption characteristics. Both a rectangular and acircular variant are depicted.

Many other shapes can be realized as well, including polygonaltransverse cross-sectional shapes, oval shapes, and (partial)combinations of such. It may have flat sides for maximum coupling ofpump light from the LEDs into the converter.

In embodiments within this class of configurations, a cylindrical, oval,or polygonal (transverse cross-sectional shape) converter (or somecombination thereof) is applied with a pump-light absorbing wallthickness significantly smaller than half the outer diameter of the rod.The thinner the wall, the smaller the extinction losses as the 4 escapecones of converted light that are associated with the 4 sides of asquare or rectangular rod are reduced down to only 2 escape cones for avery thin pump-light absorbing circular shell.

In alternative embodiments, the center body of the luminescentconversion bar/rod has a different luminescent emission spectrum thanthe shell of the body. For maximum converted light guidance performance,the center rod preferably has an absorption length much smaller than acharacteristic diameter, while also the thickness of the outer layer issmall compared to a characteristic diameter of the bar/rod. See FIG. 8b, which shows a monolithic poly-crystal ceramic bar or rod comprising aluminescent outer layer and a luminescent inner part; both parts havesubstantially the same refractive index and coefficient of thermalexpansion, but different emission spectra by differences in hostcomposition and/or activator concentration. Both a rectangular and acircular variant are depicted. The different luminescent materials 120are indicated with references 120′ (shell) and 120″ (core).

In embodiments, a monolithic poly-ceramic luminescent converter bodywith light extractor is proposed. For increasing light extraction alight extractor is applied to the luminescent converter bar/rod; thismay be a collimating type of extractor, e.g. with an outer shape as thatof a compound parabolic concentrator (CPC), or a dome type of extractor.Typically the light extractor and the luminescent converter body areconnected by an intermediate (optically transparent) medium with arefractive index somewhere in between the refractive indices of thecomponents. Some variants are displayed in FIG. 8c , which shows amonolithic polycrystalline ceramic body with luminescent outer shell anda non-luminescent core (i.e., with a core that does not absorb the pumplight), to which a light extractor is glued (top) (see also FIGS. 8a-8b). Alternatively, the center part of the poly-crystal body is alsoluminescent, but emitting a different spectrum as the outer shell(bottom) (see also FIGS. 8a-8b ). Cross sectional shapes of the bar/rodand of the light extractor may vary; depicted are rectangular (left ofthe two right figures) and round shapes (right of the two rightfigures). The optical element, here e.g. a massive light extractor, isindicated with reference 24.

In specific configurations, a rectangular light extractor is combinedwith a round luminescent converter, combining the preferred light exitwindow for a projection system with the preferred round luminescentconverter shape for maximum (light extraction) efficiency; see FIG. 8d ,which shows a combination of a circular luminescent converter body witha rectangular light extractor to match a preferred spatial extent of thelight source for specific projection applications.

In embodiments, a monolithic poly-crystalline luminescent concentratorcomprising a poly-crystalline converter body sintered together with apoly-crystalline light extractor is proposed. For maximum lightextraction as well a maximum robustness the light extractor is made of apoly-crystal ceramic as well as the luminescent converter bar/rod, andthese are co-sintered into a single monolithic light concentrator. Thematch in refractive index of the light extractor with the luminescentconverter bar/rod without any other material in between enables maximumlight extraction, while the co-sintering also results in an extremelystrong component. Tuning of the composition(s) of the converter bar/rodand the light extractor is important to achieve a scatter-free sinteredinterconnect. See FIG. 8e for some graphical representations, whereinsome configurations options for a monolithic poly-crystallineluminescent concentrator, comprising a luminescent converter rod/barco-sintered with a poly-crystalline ceramic light extractor. The wholebody has substantially the same refractive index, but localizeddifferences in activator concentration or in host composition of thegarnet material are included by design. The optical element 24 may e.g.have a rectangular cross-section (left of the three right figures),circular (middle of the three right figures), and rectangular (right ofthe three right figures); the body 100 may e.g. have a rectangularcross-section (left of the three right figures), circular (middle of thethree right figures), and circular (right of the three right figures).

For ease of manufacturing, in particular polishing, a conical or doublewedge shaped light extractor may be applied rather than a CPC-shapedextractor. Although there will be some increase of étendueendue, andtherefor reduction of radiance at the exit window, the advantages of asimpler and cheaper surface finish process may be dominating.

In embodiments, a monolithic poly-crystalline luminescent concentratorcomprising a poly-crystalline converter body sintered together with apoly-crystalline light mixing extension is proposed. For homogenizationof the spatial light distribution it can be advantageous to use anextension of the luminescent conversion body as a homogenizing lightpipe before extracting and projecting the light. In a preferredconfiguration this extension is realized by co-sintering of apoly-crystalline ceramic extension of the converter with the luminescentconverter. In a preferred class of embodiments this is further extendedwith a co-sintered light extractor. See FIG. 8f for some graphicalrepresentations of these embodiments, wherein monolithicpoly-crystalline luminescent converter with co-sintered poly-crystallinehomogenization section as extension of the luminescent converter rod/bar(top) and with additionally a co-sintered poly-crystalline lightextractor (bottom) are displayed. Reference 113 indicates ahomogenization or mixing element, configured to mix the luminescentlight. Here, the second face or radiation exit window of the lighttransmissive body can be seen as the part where the light transmissivebody changes into the optical element. Likewise, this may apply to theradiation entrance window 211. The radiation exit window 212 has in factbecome effectively the second face or radiation exit window of theassembly of light transmissive body and optical element 24.

The light extractor part may be co-molded, co-casted, or 2-k extruded,or may be molded as a separate individual part that subsequently isco-sintered with the luminescent converter body to form a singlemonolithic poly-ceramic body. Other combinations of shapes, lightabsorption distributions, and spatial distributions of emission spectraare possible using the various options for components as presentedbefore.

In embodiments, a monolithic poly-crystalline 3-D shaped luminescentconcentrator comprising a 3-D shaped poly-crystalline converter bodysintered together with a poly-crystalline light extractor is proposed.For minimization of the étendueendue of the light source, or formaximizing light coupling into the light converter, or for optimizingthe spatial extent of the light source for the application, it may beadvantageous to let the cross-sectional dimensions of the luminescentconverter/light pipe change with position (along the optical axis).Obviously this can only be realized by molding, pressing, or casting ofthe body. Thickness of the outer shell of highly absorbing luminescentmaterial as well as the diameter of the luminescent rod/bar may varywith longitudinal position. Using the approach of a monolithicallysintered body as described above, but with varying cross-sectionalshapes, enables realization of the highest efficiencies thanks toabsence of scattering at the interfaces and a continuous refractiveindex across the whole component.

The term “substantially” herein, such as in “substantially all light” orin “substantially consists”, will be understood by the person skilled inthe art. The term “substantially” may also include embodiments with“entirely”, “completely”, “all”, etc. Hence, in embodiments theadjective substantially may also be removed. Where applicable, the term“substantially” may also relate to 90% or higher, such as 95% or higher,especially 99% or higher, even more especially 99.5% or higher,including 100%.

Where stated that an absorption, a reflection or a transmission shouldbe a certain value or within a range of certain values these values arevalid for the intended range of wavelengths. Such, if stated that thetransmission of an elongated luminescent light transmissive body isabove 99%/cm, that value of 99%/cm is valid for the converted lightrays, while it would be clear to the person skilled in the art that thetransmission of an elongated luminescent light transmissive body will bewell below 99%/cm for the range of wavelengths emitted by the lightsources 10, since the source light 11 is intended to excite the phosphormaterial in the elongated luminescent light transmissive bodies suchthat all the source light 11 preferably is absorbed by the elongatedluminescent light transmissive bodies instead of highly transmitted. Asindicated above, the term “transmission” especially refer to internaltransmission.

The light transmissive body is thus especially substantiallytransmissive for at least (a spectral) part of the converted light,which (also) means substantially non-scattering for at least (aspectral) part of the converted light and showing limited absorption forat least (a spectral) part of the converted light. It may however show ahigh absorption for other wavelengths, such as especially for at least(a spectral) part of the pump light, or for only (a spectral) part ofthe converted light. It may also be scattering for other wavelengthsthan (a substantial (spectral) part of the converted light.

The term “plurality” refers to two or more.

The term “comprise” includes also embodiments wherein the term“comprises” means “consists of”. The term “and/or” especially relates toone or more of the items mentioned before and after “and/or”. Forinstance, a phrase “item 1 and/or item 2” and similar phrases may relateto one or more of item 1 and item 2. The term “comprising” may in anembodiment refer to “consisting of” but may in another embodiment alsorefer to “containing at least the defined species and optionally one ormore other species”.

Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. It is to be understood that the terms so used areinterchangeable under appropriate circumstances and that the embodimentsof the invention described herein are capable of operation in othersequences than described or illustrated herein.

The devices herein are amongst others described during operation. Aswill be clear to the person skilled in the art, the invention is notlimited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.Use of the verb “to comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Unlessthe context clearly requires otherwise, throughout the description andthe claims, the words “comprise”, “comprising”, and the like are to beconstrued in an inclusive sense as opposed to an exclusive or exhaustivesense; that is to say, in the sense of “including, but not limited to”.The article “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements. The invention may beimplemented by means of hardware comprising several distinct elements,and by means of a suitably programmed computer. In the device claimenumerating several means, several of these means may be embodied by oneand the same item of hardware. The mere fact that certain measures arerecited in mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

Practical designs may be further optimized the person skilled in the artusing optical ray trace programs, such particular angles and sizes ofmicrostructures (reflective microstructures or refractivemicrostructures) may be optimized depending on particular dimensions,compositions and positioning of the one or more elongated lighttransmissive bodies.

The invention further applies to a device comprising one or more of thecharacterizing features described in the description and/or shown in theattached drawings. The invention further pertains to a method or processcomprising one or more of the characterizing features described in thedescription and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order toprovide additional advantages. Further, the person skilled in the artwill understand that embodiments can be combined, and that also morethan two embodiments can be combined. Furthermore, some of the featurescan form the basis for one or more divisional applications.

The invention claimed is:
 1. A lighting device comprising: a lightsource configured to provide light source light selected from one ormore of ultraviolet (UV), visible light, and infrared (IR); aluminescent element comprising an elongated light transmissive body, theelongated light transmissive body comprising a side face, wherein: theelongated light transmissive body comprises a luminescent material, theelongated light transmissive body has a length (L); the elongated lighttransmissive body is hollow over at least part of the length (L) therebydefining a cavity, the elongated light transmissive body comprises aradiation input face and a first radiation exit window; wherein theluminescent material is configured to convert at least part of lightsource light received at the radiation input face into luminescentmaterial radiation, and the luminescent element being configured tocouple at least part of the luminescent material radiation out at thefirst radiation exit window as converter radiation, the elongated lighttransmissive body has a first face and a second face defining the length(L) of the elongated light transmissive body; wherein the side facecomprises the radiation input face, and wherein: the second facecomprises the radiation exit window.
 2. The lighting device according toclaim 1, wherein the elongated light transmissive body has a polygonalcross-section, and wherein the elongated light transmissive bodycomprises a cavity surrounded by the elongated light transmissive body.3. The lighting device according to claim 1, wherein the elongated lighttransmissive body has a tubular shape having a cavity surrounded by theelongated light transmissive body.
 4. The lighting device according toclaim 1, wherein at least part of the cavity comprises a lighttransmissive material, differing in composition from the composition ofthe material of the elongated light transmissive body, wherein the lighttransmissive material in the cavity has an index of refraction equal toor lower than the light transmissive material of the light transmissivebody.
 5. The lighting device according to claim 1, wherein one or moreof the first face and the second face comprise a plane comprisingsurface modulations thereby creating different modulation anglesrelative to the respective plane.
 6. The lighting device according toclaim 1, further comprising an optical element optically coupled to theelongated light transmissive body, wherein the elongated lighttransmissive body and the optical element are a single body.
 7. Thelighting device according to claim 1, further comprising an opticalelement optically coupled to the elongated light transmissive body,wherein the optical element is selected from the group consisting of acompound parabolic concentrator, an adapted compound parabolicconcentrator, a dome, a wedge-shaped structure, and a conical structure.8. The lighting device according to claim 1, further comprising anoptical element optically coupled to the elongated light transmissivebody, wherein the optical element comprises a plurality of opticalfibers, optically coupled to the elongated light transmissive body. 9.The lighting device according to claim 1, comprising a plurality ofelongated light transmissive bodies, each elongated light transmissivebody comprising a luminescent material configured to convert at leastpart of a light source light selected from one or more of the UV,visible light, and IR received by the elongated light transmissive bodyinto luminescent material radiation, wherein: the elongated lighttransmissive bodies differ in one or more of (a) length (L) of theelongated light transmissive bodies, (b) type of luminescent material,(c) concentration of luminescent material, (d) concentrationdistribution over the elongated light transmissive body, and (e) hostmatrix for the luminescent material; each elongated light transmissivebody has an axis of elongation (BA); one or more of the elongated lighttransmissive bodies comprise cavities; wherein the elongated lighttransmissive bodies are configured in a core-shell configuration whereina smaller elongated light transmissive body is at least partlyconfigured in the cavity of a larger elongated light transmissive bodyand wherein the axes of elongations (BA) are configured parallel. 10.The lighting device according to claim 9, wherein the elongated lighttransmissive bodies have side faces, and wherein side faces of adjacentelongated light transmissive bodies have no physical contact or onlyover at maximum 10% of their respective surface areas.
 11. The lightingdevice according to claim 9, further comprising an optical element,wherein the optical element comprises a first wall and a second wallsurrounding the first wall thereby defining an optical element having aring-like cross-section, wherein the optical element comprises aradiation entrance window and a radiation exit window, wherein theradiation entrance window is optically coupled with the plurality ofelongated light transmissive bodies.
 12. The lighting device accordingto claim 1, wherein the first face is facetted or has one or moreoblique sides with respect to the side face.
 13. The lighting deviceaccording to claim 12, further comprising a reflective surface facingthe first face and not being in direct contact with the first face ofthe elongated light transmissive body.
 14. The lighting device accordingto claim 1, further comprising a plurality of light sources, wherein (i)one or more light sources are configured to provide light source lightto the side face of an outer elongated light transmissive body and/orwherein one or more light sources are configured to provide light sourcelight to one or more first faces, wherein the one or more first facesare end faces, and/or (ii) wherein one or more light sources areconfigured in a cavity of an inner elongated light transmissive body andconfigured to provide light source light to the side face of the innerelongated light transmissive body, wherein at least two elongated lighttransmissive bodies provide luminescent material light with differentspectral distributions, and wherein optionally the lighting devicecomprises a control system, configured to control the spectraldistribution of the lighting device light.
 15. A lighting system,comprising: one or more lighting devices according to claim 1 and, acontroller for controlling the one or more lighting devices.